We investigate the internal strain and crystallographic orientation (texture) in physical-vapor deposited metal nitride coatings of TiN and CrN. A high-energy diffraction technique is presented that uses synchrotron x rays and an area detector, and which allows the strain and intensity distributions of multiple crystallographic planes to be measured by a single x-ray exposure. Unique texture states and nonlinear sin2 ψ strain distributions are observed for all coatings investigated. Quantitative analysis indicates that existing micromechanical models can reasonably predict strain and corresponding stress for mixed-hkl reflections but are inadequate for fully describing measured data. Alternative mechanisms involving deposition-induced defects are proposed.

The relationships between coating microstructure and properties in the Cr-C-N system have been investigated as a function of composition and post-deposition annealing. Coatings of varying compositions were grown using arc-evaporation, by varying the reactive gas flow ratio fR = f(C2H4)/f(N2) from 0 to 0.2, and were found to consist primarily of the cubic d-Cr(C,N) phase. Changes in both the unstressed lattice parameter, ao, and X-ray diffraction background intensity indicate that both the carbon concentration within the d-phase and amorphous/crystalline content increases with fR. Increasing fR also decreases the magnitude of the compressive biaxial residual stress, from approximately 6 to 1 GPa, while increasing both the inhomogeneous stress and thermal stability. The elastic modulus and hardness of as-deposited coatings were determined from nanoindentation to be 320 and 23 GPa, respectively, for moderate carbon concentrations (fR=0.05). Concurrent variations in microstructure and hardness with post-deposition annealing indicate that the as-deposited hardness is significantly enhanced by the microstructure, primarily by lattice defects and related stresses (microstresses) rather than average stresses (macrostresses).

Cr-N coatings were arc-deposited at 50 and 300 V. The changes in the coating microstructure and phase content during tempering were monitored. As a result, the phase stability and activation energies for defect diffusion were determined as a function of ion energy.

Using thick plates instead of forgings in the aircraft industry for integral construction of load carrying components is becoming more and more practice. The reasons are shorter lead-times from design of a modified or totally new component to introduction in an aircraft and smaller variations in properties for plate compared to forging. The concept of integral construction also reduces the assembly time. The complex shaped components are prepared by machining pieces of thick plate. The thicker the plate the larger components can be made in one piece. Machining components from blocks of material cut from thick plate means removal of a lot of material compared to machining of near final shape forgings. A change in machining concept to high speed machining leads to higher productivity and makes thin walled sections possible to manufacture due to decreased cutting forces.

Variation of through thickness structure and properties of 7010-T7451/2 as 100, 150 and 200 mm thick plates has been investigated. Through thickness crystallographic texture, degree of recrystallisation, distribution of inclusions, chemical composition and grain size has been mapped out. The observed structure is taken into account in order to explain variations of properties like yield strength; fracture toughness and fatigue crack growth resistance. Equipment used in the work of characterising the structure has been EBSP, SEM, X-ray diffraction and optical microscopy. Equipment used for evaluating mechanical properties is screw machines, servo hydraulic machines and hardness indentors.

The plates show a strong through thickness texture gradient that influence the yield strength. The yield strength is also dependent on chemical composition and quench rate. Recrystallisation did not show any significant influence on yield strength or fracture toughness. The grain morphology together with quench rate is of importance for the fracture toughness and the fatigue crack growth resistance.

Properties of down cut milled surfaces on thin sections using a conventional machining concept and the concept of high speed machining at various cutting speeds have been compared. The same has been done for facemilled surfaces using conventional tools and inserts at cutting speeds varying from 500 m/min up to 5000 m/min. The property of most interest is the high cycle fatigue strength. The influence of surface roughness, residual stresses and hardness on the fatigue strength has been investigated. In order to try to gain a little more information about the near surface properties x-ray diffraction studies at grazing angle incidence has been undertaken.

A mapping of fatigue crack growth rates in commercial thick plates of a high strength aluminium alloy, AA7010-T7451/52, has been done. The investigated plate thicknesses were 100, 150 and 200 mm. Material from near edge and mid-width at near surface and mid-thickness has been investigated. Measurements of crack length have been perfonned using DC potential drop. Cyclic condensation is used in order to be able to investigate local crack growth after fracture. Influence of crack closure, crack branching and slow growing side cracks on fatigue crack growth rate of S-L and L-T oriented CT specimens are discussed. S-L specimens show the highest fatigue crack growth rates. Beach marks on the fracture surface due to the cyclic condensation reveals locally straight crack fronts. A difference in growth rate between near surface and mid-thickness positioned L-T specimens are found. At a nominal ΔK of - 7 MPa√m the mid-thickness samples showed a sudden crack growth rate acceleration. The result of the investigation is explained in tenns of variations in structure, which is a function of position in the plates and plate thickness.

The influence of two different machining concepts has been compared. Pockets were machined in a thick plate of AA7010-T7451 by using a high speed machining concept at three different cutting speeds and a conventional machining concept. The pockets were machined using down cut milling and of the remaining thin walls of material fatigue samples were taken out. Some high-speed machined surfaces were anodized using chromic acid in order to see if differences in fatigue properties remained after this surface process. Fatigue properties at constant amplitude and random spectra loading were tested. Properties like residual stress, surface roughness; peak broadening at grazing incidence and micro hardness of machined surfaces were investigated and correlated to the fatigue results. A low cutting speed using the high speed machining or the conventional machining concept yielded the best fatigue properties when fatigue initiation is of concern. The higher fatigue strength is not explained by the residual stresses measured at the machined surfaces using chromium and copper radiation or by the somewhat larger surface roughness. The penetration depth of the residual stresses was found to be higher at high cutting speeds. Fatigue initiation took most often place at near surface iron-rich inclusions. The points of fatigue initiation were not found to differ for different machining concepts and cutting speeds.

In this work, a variation of fracture toughness as a function of position and orientation in commercial thick plates of a high strength aluminium alloy has been investigated. Structural and mechanical property variations have been investigated in order to understand the result of the fracture toughness measurements. 100, 150 and 200 mm thick plates of the aluminium alloy AA7010 were studied. The material was averaged and stress relieved by stretching (100 and 150 mm) and cold compression (200 mm), T7451/52. The material studied is frequently used to produce load-carrying airframe components. The knowledge of fracture properties throughout the thick plates is of importance since components are machined from them. The understanding of the varying fracture properties is valuable for development of material and or processes for producing thick plate of high strength aluminium alloys. It is of course also important to know the limitations of the thick plate material and the best way to produce a certain component from a piece of the plate material. Investigated parameters influencing fracture properties are inclusions, recrystallisation, yield strength, chemical composition and quench rate.

Face milling using different commercial tools and inserts at varying cutting speeds on a high strength aluminium alloy has been performed. The surface integrity of the machined samples has been investigated in terms of surface roughness, residual stresses, hardness and peak broadening from x-ray diffraction at grazing angle incidence. Some fatigue testing of the machined surfaces has been done. The cutting chips from the different machining parameters are investigated and compared to one another. The results show a strong influence of tool insert on surface roughness, residual stress, peak broadening, and hardness profile and fatigue properties. The influence of cutting speed on the surface integrity is much smaller. The cutting speed does however influence the size and shape of the cutting chips. There is also a general decrease in peak broadening from x-ray diffraction very near the machined surface after high cutting speeds. This could be explained by a higher local heating of the work piece at very high cutting speeds.

The variation of through thickness structure and yield strength of AA7010-T7451 thick plate has been investigated. Grain sizes at different depths were determined qualitatively by using optical microscopy. Texture measurements were carried out using X-ray technique at the same depths as grain size studies and tensile property tests have been performed. EBSP techdque has been used to compare the degree of recovered and recrystallized grain structure at different depths. Tensile testing determined through thickness variations in yield strength. The well known W shape of longitudinal yield strength variation through the thickness was not observed. The influence of texture on the yield strength measured is discussed.

The scientific and technological objectives of this program are to increase the efficiency, reliability and maintainability of industrial gas turbine blades and vanes by

• developing coatings that can warrant a 50 000 h life, i.e. twice that of the usual life, of the hot components (800–1100 °C) even with the use of renewable fuels such as biomass gas or recovery incinerator gas i.e. low-grade fuels with high pollutant levels,

• characterising advanced existing coatings to assess lifetime and performance of coatings and coated materials,

• providing material coating data and design criteria to use coating as a design element,

• increasing the fundamental understanding of the behaviour of coated materials, their degradation, fracture mechanisms and engineering because of the strong need for a mechanism-based modelling of durability.

These programmes permitted the selection of two reference coatings and the development of two innovative coatings. Concurrently work has been done in order to develop corrosion, oxidation and thermo-mechanical property models. Correlations between coatings development, experimental results and calculations will be discussed.

Thermal barrier coatings (TBCs), with a thickness of 0.4 mm, are today extensively used on the hot parts of both stationary and flying jet engines. The purpose of the TBC is to protect the underlying material from high temperatures and severe thennal shock. To increase the efficiency of a jet engine, higher turbine inlet temperatures and higher pressure ratios are sought. Consequently, materials with increased insulating properties will be required and a way to achieve this is to use thicker coatings. However, standard production procedures of thick TBCs (> 1 mm) result in coatings with an insufficient thernal shock life. The aim of this work is to develop a thick thermal barrier coating withan acceptable thernal shock life.

In the present thesis, parts of the microstructure, the residual stress state, and their correlation to process parameters in thick thermal barrier coatings are described. Further, an optimised coating structure is developed to increase the thermal shock resistance of a burner can, coated with a 1.8 mm thick TBC. The studied thermal barrier coatings, plasma sprayed onto a nickel-based substrate material, consist of a bond coating and a top coating. The bond coating material is an MCrAlY alloy and the top coating material is made of Zr0₂, partially stabilised with 8 wt.% Y₂0₃. The spraying of the coatings is perforned at Volvo Aero Corporation. Residual stresses in the samples were measured with a layer removal technique and the stresses were compared to modelled stresses from a finite element model.

Tensile stresses in the order of 150 MPa were measured in the bond coating, after the bond coating deposition. These stresses remained after the spraying of the top coating, where low stresses varying from -15 to 10 MPa were found, dependent on spraying conditions. The low stresses were a result of stress relaxation by microcrack formation. The compressive top coating stresses were found in samples where the substrate temperature was high at the end of the topcoating spraying. This gave a large temperature difference when cooling to room temperature, and due to different thermal expansion coefficients between the substrate and the top coating, more compressive stresses resulted. Good agreement between modelled and measured residual stresses was obtained. Columnar grains were found in the solidified droplets (splats) of the top coating. Between the splats, horizontally oriented delaminations were found. Top coatings sprayed at a high substrate temperature or a high passage thickness showed the columnar grains to extend through the thickness of each lamella. This decreased the density of horizontal delaminations. The density of vertical microcracks was also found to decrease as the substrate temperature increased. This was confirmed from the modelling, where the top coating inelastic strain showed the same behaviour.

Also, a segmentation crack network was found in top coatings sprayed with a high substrate temperature or a high passage thickness. The thermal shock performance of a burner can containing a 1.8 mm thick segmented top coating was compared to a can sprayed according to standard procedures. Within 35 thernal shock cycles, the standard burner can contained cracks which were considered to be unsafe for the integrity of the can. No such cracks were found in the segmented structure after 1000 cycles.

The study shows that thick thermal barrier coatings on real components can be used in jet engines provided that the correct structure is chosen.

Increased performance:cost ratios for PM steel components is vital if current growth rate of market shares of such components versus competing technology is to be sustained. Both performance and cost of components are affected by variation of component properties. This work focuses on variation; where major variation sources lie and measures to circumvent problems that could be taken.

A design-of-experiments approach was used to identify the most important green compact variations and interactions of a Fe-P alloy. The results show that the highest impact energies are obtained for high green densities, and without graphite addition. It is concluded that sintered density is the reason for the observed impact energies. Variation sources controlling phosphorus content and added graphite content are of concern since they affect the dimensional stability. Prospects for a robust sintering operation of same alloy is investigated. The objective is to find a setting of the variables investigated to maintain high tensile strength and proof stress without loss of dimensional stability, tensile elongation or impact energy. In the study, an endothermic sintering atmosphere was better for the robustness of the tested properties. A mechanism for the occasionally brittle behavior of the system is concluded to be loss of grain boundary cohesion due to decarburization.

Possibilities for improved particle size distribution of water atomized powder are studied experimentally and by simulations. The most important variable for all studied responses is water pressure. Higher melt temperatures reduce particle size due to decreased viscosity. Large sulfur additions reduce particle size and this is an effect of reduced surface tension. Narrower size distributions were obtained for powder atomized with aluminum additions and for increased melt temperatures. A model for particle size for water atomization is presented and used in simulations.

Thermal barrier coatings (TBC) are applied on hot components in airborne and land-based gas turbines when higher turbine inlet temperature, meaning better thermal efficiency, is desired. The TBC is mainly applied to protect underlying material from high temperatures, but also serves as a protection from the aggressive corrosive environment.

Plasma sprayed coatings are often duplex TBC's with an outer ceramic top coat (TC) made from partially stabilised zirconia - ZrO₂ + 6-8% Y₂O₃. Below the top coat there is a metallic bond coat (BC). The BC is normally a MCrAlX coating (M=Ni, Co, Fe ... and X=Y, Hf, Si ... ). In gas turbine components exposed to elevated temperatures nickel-based superalloys are commonly adopted as load carrying components. In the investigations performed here a commercial wrought Ni-base alloy Haynes 230 has been used as substrate for the TBC. As BC a NiCoCrAlY serves as a reference material and in all cases 7% yttria PS zirconia has been used. Phase development and failure mechanisms in APS TBC during service-like conditions have been evaluated in the present study. This is done by combinations of thermal cycling and low cycle fatigue tests. The aim is to achieve better knowledge regarding how, when and why thermal ban'ier coatings fail. As a fmal outcome of the project a model capable of predicting fatigue life of a given component will help engineers and designers of land based gas turbines for power generation to better optimise TBC's.

In the investigations it is seen that TBC life is strongly influenced by oxidation of the BC and interdiffusion between BC and the substrate. The bond coat is known to oxidise with time at high temperature. The initial oxide found during testing is alumina. With increased time at high temperature Al is depleted from the bond coat due to interdiffusion and oxidation. Oxides others than alumina start to form when the Al content is reduced below a critical limit. It is here believed that spinel appears when the Al content is lowered below 2w/o in the bond coat. Here it was shown that a faster growing oxide, rich in Ni, Cr and Co forms at the interface. Al depletion is also linked to BC phases. Initially the bond coat is a γ/ß-material possibly with very fine dispersed γ'. Simultaneously with Al-depletion the ß-phase is found to disappear. This occurs simultaneously with the formation of spinel. However, oxidation is not only a disadvantage. Low cycle fatigue tests reveal that oxide streaks within the bond coat will slow down crack growth due to crack deflection and crack branching. Therefore benefit of or damage from oxide growth on crack initiation and propagation is dependent on crack mode, spalling of the ceramic TC or growth of "classic" cracks perpendicular to the surface.

From the observations conclusions are drawn regarding fatigue behaviour ofTBC systems. The basic idea is that all cracks leading to failure initiate in the thermally grown oxide (TGO). Following the initiation, they can, however, grow to form either delamination cracks leading to top coat spallation or cracks transverse to the surface leading to component failure.

Industrial and air-borne gas turbine hot components suffer from creep, oxidation, corrosion and microstructural degradation if not shielded from the hot and aggressive combustion gases. Two major strategies commercially available are adopted; film cooling by pressurised air and application of protective coatings. Protective coatings form a slow-growing oxide that protects from oxidation and corrosion. By application of a thermal insulator, a thermal barrier coating, the material will be protected from high temperature through good insulation properties of the coating system.

If thermal barrier coatings are to be used in situations where capabilities and possibilities for inspections are limited, better knowledge of the fatigue properties of the coatings is also needed. Therefore development of a reliable fatigue life model is needed. The present work aims at serving as a basis from which a general physically founded thermal barrier coating life model can be formulated. The effects of exposure to high temperatures and mechanical loads on thermal barrier coatings under service like conditions have been investigated in the present thesis. Emphasis is put on the coupling between materials science and solid mechanics approaches in order to establish a better knowledge concerning degradation mechanisms and fatigue life issues than what is common if only one discipline is explored.

Investigations of material exposed to isothermal oxidation and thermal cyclic fatigue were performed on plasma-sprayed systems with NiCoCrAIY or NiCrAIY bond coats and yttria partially stabilised zirconia top coats. It has been shown that the thermally grown oxide that will form upon high temperature exposure influences the failure behaviour. If the oxide is composed mainly of alumina, the fatigue properties are good since the adhesion between the ceramic top coat and the metallic bond coat is good. This is also shown in a comparison between different plasma sprayed thermal barrier coating systems. If the oxide formed is based on alurnina and spinel is avoided the fatigue properties benefit from a relatively flat interface where out-of plane stresses are low in comparison to a rough interface between top- and bond coat. These findings indicate that the bonding in air-plasma sprayed systems is dependent on so called chemical bonding if the thermally grown oxide is not voluminous with high growth stresses.

It is possible to establish a fatigue life model for thermal barrier coatings. This has been shown with a model based on a modified Paris law formulation. The formulation needs to be modified with regards to mode rnixity of growth. Results achieved in the present project show that it is possible to extract crack growth data for interfacial crack growth. However a combination of mechanical testing and finite element modelling is needed since the load situation in critical areas cannot be measured. Crack growth results are presented and crack growth data are compared to predictions with good agreement.

Thermal barrier coatings are widely used in air-borne and land-based gas turbines. In these applications they serve as thermal insulators in hot components (burner cans/liners, turbine vanes and turbine blades). The present paper is aimed to describe the failure mechanism of a vacuum plasma sprayed thin thermal barrier coating system. Also the coating degradation mechanism (delamination followed by spallation) in terms of interfacial crack growth data is investigated and presented. In the present paper a 200 µm thick NiCrAlY bond coat was chosen together with a 350µm thick 7wt% yttria stabilised zirconia top coat. The coating system was exposed to thermal cyclic fatigue with a thermal cycle ranging from 100 °C to 1100 °C and a cycle time of 70 minutes. After thermal cyclic testing all specimen were subjected to standard sample preparation routines and inspected by optical microscopy and scanning electron microscopy. In order to describe interfacial crack growth an interface damage measure is used. For the present coating system under current thermal load conditions a mainly black interface fracture is discovered. The top coat exhibit microcrack formation after thermal fatigue, but these cracks do not contribute to the final fracture appearance. Crack growth rates are compared to local stress intensity levels at the top coat / bond coat interface. From crack length measurements are crack growth data da/dN = f(ΔK_eff) calculated.

An air plasma sprayed thermal barrier coating was investigated in order to clarify links between heat treatment, oxidation and diffusion behaviour. In the study a thin Zirconia (PSZ) layer was used as top coat together with a NiCoCrAlY bond coat. The investigation was focused on differences for three geometries. Thermal barrier coatings on flat, concave and convex surfaces were studied. Isothermal oxidation was performed up to 1000 hrs at 1000°C in order to simulate true working conditions for the interface between ceramic top coat and metallic bond coat. The investigations show presence of Al-rich oxides for shorter times. When the coating system is heat-treated for 1000 hrs a change of oxide composition is obvious and beside Al the oxides contain Ni, Cr and Co. The oxides tend to grow with different rates depending on the macroscopic surface geometry. In the study convex surfaces reveal the highest oxide growth rates and concave the lowest growth rates. At 1000 hrs and 1000°C the difference between the fastest and the slowest growing oxide layer is 1 μm. Some interdiffusion is obvious. Between the superalloy substrate and the bond coat outward diffusion of Ni, W and Cr is present together with inward diffusion of Co and to some extent Al.

An air plasma sprayed thermal barrier coating was investigated in order to clarify links between heat treatment, oxidation and diffusion behaviour. In the study a thin Zirconia (PSZ) layer was used as top coat together with a NiCoCrAIY bond coat. The investigation was focused on differences for three geometries. Thermal barrier coatings on flat, concave and convex surfaces were studied. Isothermal oxidation was performed up to 1000 hrs at 1000°C in order to simulate true working conditions for the interface between ceramic top coat and metallic bond coat. The investigations show presence of Al-rich oxides for shorter times. When the coating system is heat-treated for 1000 hrs a change of oxide composition is obvious and beside AI the oxides contain Ni, Cr and Co. The oxides tend to grow with different rates depending on the macroscopic surface geometry. In the study concave surfaces reveal the highest oxide growth rates and convex the lowest growth rates. At 1000 hrs and 1 000°C the difference between the fastest and the slowest growing oxide layer is 1µm. Some interdiffusion is obvious. Between the superalloy substrate and the bond coat outward diffusion of Ni, W and Cr is present together with inward diffusion of Co and to some extent Al.

In the present study the influence of bond coat composition and coating process on thermal barrier coating (TBC) life has been evaluated. Six different coatings have been subjected to thermal cycling between 100 and 1100°C. After this the different systems have been characterised by light microscopy and SEM-EDS. Various commercial bond coats have been applied on one substrate material (Haynes alloy 230). The total fatigue life of the different TBC systems varies with 30% what is believed to be influenced by diffusion and oxidation phenomena in the bond coat. It is found that when the aluminium concentration is decreased phases other than alumina form at the top coat I bond coat interface. Oxides formed during later stages of the thermal cyclic test are rich in nickel, cobalt and chromium and the results can be interpreted as formation of nickel-, chromium- or spinel oxides. The reason for TBC failure is coupled to aluminium depletion, which here is believed to be due to inward diffusion and formation of thermally grown oxides (TGO) at the ceramic top coat (TC) metallic bond coat (BC) interface as well as growth of internal oxides in the bond coat.

In the present study the influence of bond coat composition and coating process on thermal barrier coating (TBC) life has been evaluated. Six different coatings have been subjected to thermal cycling between 100 and 1100°C. After this the different systems have been characterised by light microscopy and SEM-EDS. Various commercial bond coats have been applied on one substrate material (Haynes alloy 230). The total fatigue life of the different TBC systems varies with 30% what is believed to be influenced by diffusion and oxidation phenomena in the bond coat. It is found that when the aluminium concentration is decreased phases other than alumina form at the top coat / bond coat interface. Oxides formed during later stages of the thermal cyclic test are rich in nickel, cobalt and chromium and the results can be interpreted as formation of nickel-, chromium- or spinel oxides. The reason for TBC failure is coupled to aluminium depletion, which here is believed to be due to inward diffusion and formation of thermally grown oxides (TGO) at the ceramic top coat (TC) metallic bond coat (BC) interface as well as growth of internal oxides in the bond coat.

The relation between the process and mechanical properties in aluminium alloys for castings has been examined. The relation was hard to define since the spread in data was severe due to defects created in the casting process. To avoid such defects a gradient solidification equipment was built. With this equipment it is possible to re-melt and solidify meta! with good feeding during the solidification over a !arge range of solidification rates. The results show very good mechanical properties for several cast aluminium alloys. From this it is concluded that the casting processes used today are not designed in a way that utilises the inherent potential in mechanical properties of the material.

The ingate system design has been found to be one of the most important factors that influence the mechanical properties in castings. In this work many experiments have been made in order to study the mould filling behaviour. By the use of a glass wall and a video camera the mould filling of a vertically parted vacuum-sealed sand mould was studied. By changing the ingate system design and studying the filling sequences a thorough knowledge of the melt behaviour in the ingate system during the filling of the mould could be obtained. This knowledge could be used in many foundries to improve the ingate system design in order to increase the quality ofthe castings.

A filter in the ingate system has been found to be one of the best ways to improve the mould filling. The filter will however reduce the flow, rate and it is therefore important to know the magnitude of the flow reduction. In this work a new technology is presented which can be used to obtain optimum proper filter parameters, which are important to get accurate results from simulations.

Fundamental and technological aspects of fatigue and fracture of conventional and advanced material are topics of primary importance to the development of materials science and engineering. Surface treatments have been established to improve the surface properties of material against surface phenomenon such as wear, corrosion, fatigue and corrosion fatigue. This thesis deals with the influence of two modem (plasma nitriding and laser hardening), and one conventional (hot dip galvanizing), surface treatments on the fatigue, corrosion fatigue (in seawater) and fracture of a B-Mn steel. The main approach adopted here focuses the attention on fatigue crack initiation mechanisms.

Constant stress amplitude plane reversed bending fatigue tests (R = -1) at room temperature and at a frequency of 47 Hz in air and sea water were conducted using cylindrical untreated and surface treated quenched and tempered (Q&T) steel specimens made of a B-Mn SS2131(∼AISI 15B21H) steel with stress concentration factors of K_t =1.05 and 1.7.

S-N curves show that surface treatments improved the fatigue limit by 53 % and 115 % (plasma nitriding), and 18% and 56 % (laser hardening) of smooth and notched Q&T specimens; whereas hot dip galvanizing slightly decrease the air fatigue limit of smooth (-9 %) and notched (-10 %) Q&T specimens. The small cracks formed in the coating during galvanizing could be the cause of this reduction. Compressive stresses and improved strength (hardness) introduced by plasma nitriding and laser hardening play the principal role for the improvement of fatigue strength, subsurface crack nucleation, fish-eye asymmetry, and reduction of stress intensity factors. Plasma nitrided (PN) and laser hardened (LH) materials behaves as composites. Laser process parameters have to be optimised in order to avoid the formation of a damaged area (characterised by a low hardness and low compressive residual stresses) around the overlap zone which promotes the formation of long narrow crack along the edge of the overlap zone causing premature failure.

Sea water suppress the fatigue limit and reduces fatigue strength (especially at long lives) of smooth and notched Q&T, PN and LH specimens, but smooth and notched hot dip galvanized (HDG) specimens still exhibit a corrosion fatigue limit (at 2x10⁷ cycles) with values a little lower than the corresponding air fatigue limits. Physical and electrochemical corrosion protection by hot dip galvanizing are the causes for the good corrosion fatigue properties obtained. Plasma nitriding improves the corrosion fatigue resistance of Q&T specimens; it is associated to the good corrosion resistance of ε and -phases, the enhancement of corrosion and fatigue by compressive residual stresses and the consumption of H⁺ ions during reduction of nitrogen. Mechanisms for nucleation of pits, and corrosion fatigue cracks have been proposed to explain corrosion fatigue strength reduction due to sea water. A derived equation predict well the corrosion fatigue strength of notched specimens from the observed air fatigue strength of smooth specimens.

The meta! expansion penetration has been examined experimentally. The whole casting process was simulated using a commercial software, in order to investigate the solidification characteristics and the pore formation in the casting studied. In order to do this, a special module for cast iron was used, where nucleation and growth of all relevant phases are considered. During simulation it is possible to detect the areas where porosities are likely to be formed. The results of the experiments show that expansion penetration generally occurs in the same areas as detected in the simulation depending on the solidification path. The inoculation and solidification behaviour will result in an excess or deficiency of meta! at the end of solidification. This will lead to either meta! penetration or the formation of pores.

A series of test castings were produced at a foundry. They were used to study the influence of chemical composition, the type and amount of inoculant and the casting temperature. The results show that the carbon and phosphorus content had an influence on meta! penetration. The tendency for meta! penetration decreased whit decreasing carbon content as well as with increasing phosphorus content.

The experiments show that the type and amount of inoculant and casting temperature for grey cast iron influence the meta! expansion penetration in areas with late solidification and where the melt is in contact with the sand mould. The worst cases of meta! penetration were obtained with uninoculated melt. A !arge number of small eutectic cells making up a !arge fraction of the volume were observed, resulting in a !arge penetration.

With contributions from 24 authorities from around the world, this handbook provides the most authoritative reference resource available on the impact of residual stresses on mechanical properties of materials and structures. You'll find detailed descriptions of a full range of measuring techniques, including hole drilling, layer removal, sectioning, X-ray diffraction, neutron diffraction, and ultrasonic methods. A variety of case studies which illustrate use of specific techniques are included to facilitate your understanding. Design and structural engineers, metallurgists, and material scientists will find a wealth of valuable information covering recent developments in residual stress measuring techniques, with guidelines provided for selecting the right measuring strategy for each specific application, and many helpful tips for improving quality control.