摘要:

AbstractThe changes in composition of the grain boundary regions in Nimonic PE16, which occur during heat treatment and on neutron irradiation, are described. The results show that the composition of these regions is sensitive to heat treatment variables, bulk composition, and irradiation. In particular, molybdenum has a strong tendency to segregate to grain boundaries both on cooling from solution treatment and on aging. The non-equilibrium segregation which occurs on cooling increases with increasing boron content of the alloy. Chromium also segregates to grain boundaries under these conditions, though there is no dependence on boron content. Aging at 700°C causes molybdenum and chromium to segregate to grain boundaries until the onset of precipitation of M23C6, M6C, and Laves phase causes a decrease in the concentrations of these elements. The effects of neutron irradiation are dependent on the boron content of the alloy.MST/1336

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.385

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractAn investigation has been made of the constitution of the titanium rich partial Ti–V–Fe–Al system in the composition range applicable to commercialα+βandβTi–V–Fe–Al alloys (e.g. Ti–10V–2Fe–3Al alloy) and at temperatures between 650 and 800°C. Partial Ti–V–Fe isothermal sections for alloys containing ~4 wt-%Al and V and Fe in a ratio≥1:1 show onlyαandβas the equilibrium phases for compositions up to 13 wt-%V and 4 wt-%Fe. The position of theα+β/βboundary is temperature dependent and its shape is affected by the amount of aluminium present in theβin equilibrium with a in the quaternary Ti–V–Fe–Al alloys. By contrast, theα/α+βboundary is independent of these parameters. Microstructural features relating to morphology and volume fractions ofαandβphases have been investigated and, together with the compositions ofαandβ, are discussed in the context of alloy properties and processing.MST/1323

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.391

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractSilicon aluminium oxynitride (β′sialon) powders have been prepared by reacting kaolin–carbon mixtures at 1400–1500°C in flowing nitrogen. The kaolin/carbon ratio in the starting mixtures must be accurately controlled to obtain single phaseβ′powders. The overall reaction rate increased with increasing nitrogen flowrate. However, if the nitrogen flowrate was too high, the amount of 15Rand AlN phases in the reaction products increased. A change of carbon source in the starting mixtures affected the phase composition as well as the morphology of the product powders. It was found that the evaporation of SiO is a most important factor in the reaction, strongly affecting the phase composition of the reaction products.MST/1346b

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.399

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effect of rapid solidification of Cu–2·3 at.-%Cr and Cu–3·1 at.-%Cr alloys by melt spinning and of subsequent aging on their electrical properties has been investigated and discussed on the basis of Matthiessen's hypothesis. Melt spinning was found to increase the chromium content in solid solution from the maximum equilibrium solubility of 0·8 at.-% to more than 3 at.-%. In this state, the variation of resistivity as a function of the chromium content appears to be a simple linear extension of the relationship obtained for Cu–Cr alloys after solid state quenching. The measurements on aged ribbons indicate that their conductivity changes from about 10% IACS in the melt spun condition to a maximum of 60% IACS in the overaged condition. The presented evaluations lead to the conclusion that the resistivity of melt spun alloys is controlled by the spacing between chromium atoms in solid solution, whereas the resistivity of these alloys after aging is controlled by the spacing between chromium particles, both of these spacings being much smaller than the mean free path of electrons in copper.MST/1252

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.407

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractTechniques and equipment were developed for the extrusion of vapour deposited RAE Alloy 72. The alloy was extruded at temperatures from 300 to 420°C and extrusion ratios from 2:1 to 25:1. Room and elevated temperature strengths and smooth S–N (stress–number of cycles to failure) fatigue properties were determined for a range of extrusions. The best extrusions gave room and elevated temperature strengths that were comparable to those of rapidly solidified aluminium alloys. The fatigue strength/tensile strength ratio of>0·5 was higher than would be expected for an aluminium alloy.MST/1350

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.410

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effects of aging treatments on the tensile properties and microstructure of Al–Cr–Zr–Mn powder metallurgy aluminium alloys prepared from high pressure gas atomised powders were investigated. The alloy compositions were designed to give powders with or without Al13Cr2intermetallics in the<45μm size fraction. The Al–5·2Cr–1·4Zr–1·3Mn alloy is typical of the former (concentrated alloy) and the Al–3·3Cr–0·7Zr–0·7Mn alloy of the latter (dilute alloy). The alloys were prepared using a canning/degassing/extrusion sequence or the Conform consolidation process. Measurements of micro hardness and electron microscopy were used to correlate the microstructure with the tensile properties. The extruded powders of both alloys exhibited better properties than those of the Conformed powders. A large contribution to the strength of the extruded materials is made by their stabilised fine grain size. The dilute alloys had consistently better ductility. Neither alloy retained its strength after prolonged aging at 400°C, but the results indicate that a service temperature of 300°C may be possible.MST/1247b

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.419

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractHigh temperature total endurance tests were conducted on three alloys (316L steel at 550°C; 9Cr–1Mo steel at 550°C; Nimonic 101 at 850°C) in low cycle fatigue under continuous cycling. The austenitic steel was observed to cyclically harden, whereas the ferritic steel and the superalloy both cyclically softened. Methods for rationalising evolutionary behaviour were variation of percentage hardening/softening with strain range, cumulative ductility criterion, variation of secant modulus in the hysteresis loops, and cumulative energy criterion. The energy expended per cycle appears to be the most attractive. For a given strain range this was approximately constant at any stage of evolution. More significantly, the cumulative energy at saturation was constant, approximately independent of total strain range, and about 0·5–3·0 J mm−3according to the material used. The Palmgren–Miner hypothesis (which is widely used in summing fatigue damage) was originally derived on an energy argument and it is proposed that calculations using values of absolute energy would have definite advantages.MST/1354

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.427

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effect of grain size on the mechanical properties of metastable Ti–15V–3Cr–3Sn–3Alβtitanium alloy has been investigated. In the solution annealed condition the small grain sized specimens are of strength higher than the large grain sized specimens. However, when the alloy is aged the large grain sized specimens become the stronger. The aged, large grain sized specimens have also improved fracture toughness. This unexpected behaviour is explained by means of models which incorporate the contributions of the grain boundaries and the grain interior to the strength and fracture toughness.MST/1365

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.441

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA 7000 series high strength aluminium alloy was produced by spray deposition via the Osprey process. This alloy, designated AlZn11MgCu, exhibits an excellent combination of fracture toughness and strength in both the peak aged T6 and overaged T7 conditions. The yield strength and fracture toughness at room temperature are 700 MN m−2and about 40 MN m−3/2in the T6 temper, and 500 MN m−2and 75 MN m−3/2in the T7 temper, respectively. The exceptional high fracture toughness is attributed to the absence of coarse constituents and oxides. The microstructure is homogeneous, free of segregation, and has a fine grain size. The hardening precipitates in the T6 temper are mainlyη′, and in the T7 temper they areη(MgZn2), resulting in a different fracture behaviour; in the T6 temper the fracture mode is microshearing and in the T7 temper the fracture mode is ductile failure. Both T6 and T7 conditions show a stress corrosion crack growth rate higher than that of comparable alloys, 7075-T651 and 7075-T7351.MST/1308

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.447

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effects of laser surface hardening on AISI 01 tool steel samples were studied by changing the laser operating parameter combinations and the initial steel microstructure. Both melted and solid state transformed regions were produced, and then studied using optical microscopy, analytical electron microscopy, X-ray diffraction, and measurements of micro hardness to investigate the hardening mechanisms and the development of compressive residual stresses. The results indicate that hardened case depths up to 0·6 mm can be obtained using a laser beam operated at a power of 500 W and a scan rate of 2·1 mm s−1, but that different amounts of retained austenite and undissolved carbides are observed for different beam powers. Quenched and tempered AISI 01 steel samples, with initial hardness values in the range 30–40 HRC, are better suited for laser surface hardening compared with the samples with initial hardness of 48–50 HRC, because the formation of an over tempered region adjacent to the hardened zone can be avoided.MST/901

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.5.452

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor