摘要:

AbstractThe standardised indentation fracture toughness equations formulated in Part 1 have been applied to a range of brittle materials: namely, glass ceramics, aluminas, zirconias, and WC–Co cermets. Analysis of the results has enabled a critical assessment of (i) the ability of the nineteen equations to yield the same fracture toughness values as a conventional fracture toughness test and (ii) their ability to rank materials in order of fracture toughness. Also, specific equations have been recommended as being the most appropriate equations to use.MST/1050b

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.961

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractIn an attempt to develop improved models for the prediction of microstructures in steel weld deposits, established thermodynamic procedures have been used to estimate the liquidus, solidus, and Ae3transformation temperatures for multicomponent steels, together with partitioning coefficients and other parameters. The method has been tested against a large amount of published data and there is found to be good agreement between experiment and theory.MST/975

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.977

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractIt is shown that microadditions of Mg to cast M17 superalloy significantly improve the impact toughness, the high cycle bending fatigue endurance, and the stress rupture properties at high temperature. There is a relationship between these improvements and Mg refinement of the MC primary carbide. Analysis using Auger electron spectroscopy shows Mg segregating to various interfaces and in particular to the carbide/matrix interface. A thermodynamic analysis of the diffusion process is presented to show that the Mg segregation results from uphill diffusion of Mg to the Ni enriched interfacial liquid surrounding the growing carbide particle, which derives from the negative excess Gibbs free energy change for the Ni(rich)–Mg liquid solution.MST/991

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.985

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe effect of microadditions of Be and Ca on the aging behaviour of Al–0·75Mg–0·5Si alloy is investigated. It is shown that the addition of 0·1%Be significantly increases the hardening rate and the maximum hardness level attainable when the alloy is aged at various temperatures from room temperature to 300°C, while the addition of 0·2%Ca decreases both the hardening rate and the maximum hardness level attainable. Optical and scanning electron microscopical observations show a significantly higher precipitate density for the Be containing alloy and a slightly lower precipitate density for the Ca containing alloy when compared with the base Al–Mg–Si alloy. The results are consistent with an earlier kinetic study that indicated a Be enhanced nucleation rate for precipitation in the same alloy.MST/936

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.991

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractTests concerning the mechanical properties of quenched aluminium were carried out on samples having different grain boundary characteristics. In comparison with aluminium of equilibrium structure, the quenched aluminium was found to be characterised by: a greater value of yield point in samples having a low fraction of special grain boundaries, and a lower value of yield point and a reduction of the Lüders strain in samples having a high fraction of special grain boundaries. The effects can be ascribed to the activity of dislocation loops as sources of dislocations or to a change in grain boundary characteristics as a result of annihilation of non-equilibrium vacancies on the grain boundaries.MST/965

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.995

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractGenerally, superplastic deformation is accompanied by concurrent grain growth. In this paper, the effect of strain reversals on this process is investigated using two materials. In the first, Coronze 638, a precipitate strengthened copper alloy, no effect is found. In the second, Zn–22Al (wt-%) eutectoid, a distinct retardation of grain growth occurs after each strain reversal. A new model based on the ability of grain boundary sliding to overcome the Zener drag process is developed and found to be consistent with the experimental results.MST/731

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.999

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractSimple equations which describe the rates of creation and annihilation of dislocations are used to predict the creep transients which follow a stress change. Behaviour can be understood most easily with reference to the functional dependence of creep rate upon dislocation network spacing. The creep rate is zero below a critical value of spacing and the function shows a maximum at some higher value of spacing. It is shown that the types of transient response depend critically on the position of the steady state creep rate with respect to the position of this maximum. Materials are considered to be divided into two categories depending on the relative mobilities of glide and climb. The wide variety of transient types that exist can all be shown to follow as a natural consequence of these considerations.MST/996

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.1005

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe dependence on temperature of the impact toughness in Al–Li–Cu–Mg–Zr alloys was investigated focusing on the low temperature impact toughness. The impact toughness of Al–Li–Cu–Mg–Zr alloys in the low temperature region (≤423 K) increased with decreasing temperature. Laminated cracks, the number of which increased with the increase in impact toughness in the low temperature region, were observed and it was suggested that the appearance of these cracks resulted in part of the increase of the impact toughness of this alloy. The spectra of potassium and sodium were detected from the fracture surface of a specimen tested at room temperature. This indicates that a low melting point metal phase seems to affect the impact toughness near room temperature, i.e. this phase seems to produce the liquid metal embrittlement locally at the grain boundary.MST/787

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.1013

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe nature of deformation in the roll gap during single pass rolling was investigated and it was found that the metal flow is complex. It was also found that the edge profile changes from a double barrel profile near the entry to a convex profile near the exit depending upon the deformation conditions. The factors affecting spread in the lateral direction were investigated in two commercial Al–Mg alloys: AA 5056 and AA 5083. The results of over 120 carefully controlled laboratory hot rolling tests were analysed with the help of the main existing spread formulae. In view of the inability of these formulae to predict closely the spread, a new formula has been derived from the experimental results.MST/961

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.1021

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractRapidly solidified powders of magnesium were produced in a pilot plant gas atomiser. Argon gas at 1·85 MPa was used as the atomising agent in a‘confined design’nozzle operating vertically upwards. Oxygen was introduced into the plant at a level of 1% to cause controlled oxidation to passivate the particles. Powders were sized using dry sieving down to 32μm and wet sieving for smaller sizes. Sauter mean diameter varied between 18·45 and 21·40μm depending on the rate of production. The distribution of sizes was typically bimodal with the separation point of the peaks at ~34μm. This supported the particle formation theory developed earlier which predicted that atomised metal powders consisted of two families of particles. The fine range of the particles was spherical up to ~30μm in diameter. In the coarse range, which was virtually free of satellites, the overall round nature of the particles was preserved, but some oblong shapes were also observed. Comparison with the atomisation of aluminium shows that, despite having a lower surface tension, magnesium powders are marginally coarser than those of aluminium produced under the same conditions. This is explained in terms of the faster acceleration of magnesium droplets (by virtue of lower density) in flight during secondary breakup.MST/915

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.10.1027

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor