摘要:

AbstractWear resistant coatings of hardfacing alloys can be produced with powders by using various techniques such as laser cladding (LC), plasma transferred arc (PTA) welding, atmospheric plasma spraying (APS), etc. The properties of coatings applied using these techniques differ slightly owing to the manufacturing process, despite having the same chemical composition. The coating microstructures and properties (such as hardness, wear resistance, and corrosion resistance) of nickel base hardfacing alloys produced by LC, PTA welding, and APS have been studied. Estimates of realistic coating thickness, coating rate, powder consumption, and the influence of temperature on the substrate material during LC, PTA welding, and APS are given.MST/1696

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.657

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractReactive sputter deposition is a widely used glow discharge process for growing high melting point coatings near room temperature, and metastable and multiphase structures not attainable in bulk material grown under conditions of thermodynamic equilibrium. It is therefore ideally suited for growing refractory metal oxide coatings. In this study,‘phase maps’are constructed for the sputter deposition of the refractory metal oxides of Nb, Y, and Zr. These diagrams interrelate process parameters, the growth environment, and metallurgical phase in the growth regime of near room substrate temperature, low surface diffusion, and sticking coefficient of unity. Phase boundaries are discussed in terms of: (i) the fractional flux of metal atoms and metal oxide molecules to the substrate; (ii) a complete oxide layer at the metal target surface; (iii) oxygen species in the plasma available for reaction at the substrate.MST/1693

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.666

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAluminide diffusion coatings are frequently employed to enhance the oxidation resistance of nickel base superalloys. However, there is a concern that the presence of an aluminide coating could influence the properties of the coated superalloy, especially in respect of fatigue behaviour. To understand the nature of the effects of surface coatings on the fatigue properties of superalloys, an understanding of microstructural development within both the coating and the coating/substrate interfacial zone during high temperature fatigue testing is necessary. This paper is concerned with microstructural changes in aluminide diffusion coatings on single crystalγ′strengthened superalloy substrates during the course of high temperature fatigue testing. The‘edge on’transmission electron microscopy technique is employed to study cross-sections of two stage (aluminisation plus diffusion treatment) coated superalloy samples. The paper examines the degradation of the coating produced by phase transformations induced by loss of aluminium from the coating and/or aging of the coating. Aluminium removal both by interdiffusion with the substrate and by oxidation of the coating surface is considered. Microstructural development in the portion of the substrate influenced by interdiffusion with the coating is also discussed.MST/1694

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.673

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe mechanical properties of diamond films deposited via hot filament chemical vapour deposition have been determined using a range of techniques, and related to the composition and morphology of the diamond films as determined by laser Raman spectroscopy. As the quality of the film increases, its hardness (as determined by the volume law of mixtures hardness model) also increases until it is larger than values often reported for polycrystalline bulk material, a consequence of the very small grain size in the films. Coating adhesion, as determined from indentation adhesion tests, also appears to improve with coating quality. Variations in the behaviour of the friction coefficient between diamond films and diamond and steel counterfaces are less well defined, but it appears that the surface morphology of the film is important in dictating the behaviour rather than the quality of the diamond. These results are discussed in the context of the potential use of diamond coatings in tribological applications.MST/1695

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.679

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThis paper presents an overview of duplex stainless steels (DSS) with particular emphasis on super DSS, i.e. steels containing sufficient amounts of chromium, molybdenum, and nitrogen to produce a pitting resistance equivalent greater than 40. Duplex stainless steels have an attractive combination of mechanical and corrosion properties and are thus suitable for many marine and petrochemical applications, particularly where chlorides are present. The paper covers the following aspects of DSS: physical metallurgy, mechanical properties, corrosion properties, metallurgy of welding, machinability, and applications. A large number of references to the literature are given to aid the reader who is interested in acquiring a deeper understanding of the behaviour of this family of steels.MST/1685

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.685

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe effects of micro additions of vanadium and boron on the age hardening, microstructure, mechanical properties, deformation, and fracture behaviour of Al–Li alloy 8090 have been investigated. The addition of 0·6% V to 8090 alloy increases the peak hardness by 13%, the yield strength by 23%, and the ductility by 85% when optimally aged (190°C for 22·5 h). The enhancement of these properties is attributed to the refinement of S′andδ′precipitates and the promotion of extensive cross-slip during deformation of the vanadium containing alloys. The same amount of vanadium reduces the impact toughness of 8090 by 50%, which is attributed to the presence of coarse particles of primary Al11V precipitate. Increasing the cooling rate during solidification, or adding 0·1%B, restores and slightly increases the impact toughness of the vanadium containing alloy. The effect of cooling rate is related to the amount and size of Al11V precipitates, which decrease with increasing cooling rate. The addition of boron appears to modify the morphology of the Al11V precipitate.MST/1584

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.701

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAluminium alloys containing additions of iron and cerium are among the alloys being developed as potential replacements for titanium based alloys for moderately high temperature applications. Development of these alloys is possible using rapid solidification technology, which results in a very fine distribution of dispersoids in the aluminium matrix. The microstructures of two rapidly solidified high temperature alloy powders of composition (wt-%) Al–6·7Fe–5·9Ce (alloy A) and Al–6·2Fe–5·9Ce–1·63Si (alloy B) have been characterised using transmission electron microscopy and the results are explained on the basis of some of the major solidification parameters, such as nucleation undercooling and recalescence. It was observed that most of the powder particles in the +10 to−20μm size range contained both microcellular and cellular regions, which could be explained in terms of an initial large undercooling followed by recalescence. The decomposition of the powder microstructure after exposing the powders to temperatures of 350, 420, and 500°C for 1 h was investigated using transmission electron microscopy. This work was complemented by phase identification studies using X-ray diffraction. The equilibrium precipitates Al13Fe4, Al8Fe2Si, and Al3FeSi were detected in the powder microstructure of alloy B, whereas Al13Fe4precipitates were detected in alloy A after high temperature exposure (500°C).MST/1571

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.709

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe influence of helium on the diffusion at a migrating boundary has been investigated during discontinuous precipitation in a Co–14 at.-%Al alloy and during discontinuous dissolution in an Al–15 at.-%Zn alloy. The helium was introduced into the alloys via a plasma treatment using various fluxes. Two opposing processes have been observed depending on the flux. One, below a critical flux, led to an increase in the linear growth rate of discontinuous precipitation and discontinuous dissolution owing to an enhanced concentration of vacancies, which acted as carriers of solute atoms in the diffusion process. The other process, above the critical flux, resulted in the appearance of helium bubbles, which acted as mechanical obstacles to the moving discontinuous precipitation and discontinuous dissolution front and as sinks for the excess vacancies. The effect of helium on the diffusion ahead of the advancing front during discontinuous precipitation and discontinuous dissolution has been well described using a parameter DbAl or Zn/DVHeproposed by the authors.MST/1531

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.716

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe type of abrasion that the grinding medium experiences inside a ball mill is classified as high stress or grinding abrasion, because the stress levels at the surface of the medium exceed the yield stress of the metal when hard abrasives are crushed. During dry grinding of ores the medium undergoes not only abrasion but also erosion and impact. As all three mechanisms of wear occur simultaneously, it is difficult to follow the individual components of wear. However, it is possible to show that the overall kinetics of wear follows a simple power law of the type w = atb, where w is the weight loss of the grinding medium for a specified grinding time t and a and b are constants. Experimental data, obtained from dry grinding of quartz for a wide range of times using AISI 52100 steel balls having various microstructures in a laboratory scale batch mill, are fitted to the proposed equation and the wear rate w is calculated from the first derivative of the equation. The mean particle sizes of the quartz charge D corresponding to 50 and 80% retained size are determined by mechanical sieving of the ground product after a grinding time t and thus the relationship between wear rate and particle size of the abrasive is established. It is found that w increases rapidly with D up to some critical size and then increases at a much lower rate.MST/1620

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.722

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractSpecimens of commercially available Superalpha 2 were solution heat treated at 1060°C in the (α2+βphase field, air cooled, then aged at temperatures between 650 and 950°C followed by air cooling. During aging, the B2 phase was more stable than expected from earlier work. The aged specimens were tensile tested to failure at room temperature and microstructural studies were carried out using optical microscopy, scanning electron microscopy, and analytical transmission electron microscopy. It was found that the strength of Superalpha 2 could be dramatically increased by aging at low temperatures, which refines theβmatrix. The ductility at room temperature was observed to depend on the volume fraction of retained B2 phase.MST/1578

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.8.729

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor