摘要:

AbstractThe microstructure of unidirectionally solidified Cd–CuCd3eutectic monovariant alloys containing elemental additions of Zn, Mg, and Pb was studied. The addition of either Mg or Pb resulted in changes of eutectic morphology, such as curving and branching of CuCd3rods, which could be directly attributed to the formation of eutectic cells. The addition of Zn led to microstructural modifications even when the solid/liquid interface was macroscopically flat. Such modifications included an increase of interrod spacing, the stabilisation of a rod morphology at a velocity which produced a mixed blade–rod morphology in the pure eutectic, and the protrusion of CuCd3phase at the solid/liquid interface. These modifications were attributed to a change of faceting behaviour of the CuCd3phase by the addition of Zn. It is proposed that the formation of lateral facets on the CuCd3changed the growth mechanism at the solid/liquid interfaces effecting the modifications described.MST/1009

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.1

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe diffusion of59Fe in Incoloy 800 has been studied using the serial sectioning technique in the temperature ranges 1020–1500 K for volume diffusion and 750–1100 K for grain boundary diffusion, respectively. The volume diffusion coefficients can be represented by the expression: D(1020–1500 K)=3·26×10−5exp (−259·6 kJ mol−1/RT) m2s−l. The grain boundary diffusion coefficients were evaluated in most of the experiments using Whipple's method. For afew specimens, Suzuoka's method was applied. The penetration depths beyond which these methods were to be applied to analyse the experimental results were determined both graphically and by extensive use of autoradiographic techniques. The grain boundary diffusivities can be expressed as: Dgb(750–1100 K)=1·88×10−5exp (−160·7 kJ mol−1/RT) m2s−1, The results are discussed and presented in this paper.MST/l193

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.8

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractMicrotextures have been measuredfor compressed and annealed nickel which, since the data arose from contiguous grains, allowed the mesotexture–the texture between grains–to be collated. Nearly 2400 grain boundaries were included in the part of the study reported here. The microtexture and accompanying macrotexture showed a very weak compression fibre texture which became slightly more well defined after annealing. The mesotexture, assessed in terms of proximity to coincident site lattice (CSL) misorientations showed a bias towards low-ΣCSLs (Σ=3 to 15) rather than high-ΣCSLs (Σ=17 to 35). As annealing and grain growth proceeded,Σ=3nboundaries (n=1 to 3) became more prevalent in the mesotexture. A second nickel sample which had been annealed at a high temperature before compression had a mesotexture which was dominated byΣ=3nboundaries. The differences between the two specimens was attributed to differences in impurity levels.MST/1307

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.12

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA method based on Rutherford back-scattering ofα-particles was used for the investigation of tin coatings electrolytically applied to low carbon steel strip. The method allowed the investigation of the distribution of tin atoms through the thickness of the coating to a depth of a few micrometres. The results obtained show that the treatment applied to prepare the steel surface for coating has a marked effect on the final composition of the deposited layer. In particular, the omission of the final water rinsing led to the formation of a denser layer and, as a result, to an increased corrosion resistance of the coated strip.MST/1172

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.20

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe iron oxide which predominates inferritic stainless steel conversion coatings for photothermal conversion is a chromium substituted magnetite (Fe2+Fe3+2−xCr3+x)O2−4: the chromium content of this magnetite could be at least that of the stainless steel substrate (x≥0·5). This substituted magnetite coexists with a partially oxidised magnetite. The thermal treatment of these coatings induces theformation of the corundum type phaseαFe2O3by oxidation of the substituted magnetitefrom 175°C. At higher temperatures, FeCr2O4andαFe6−yCryO9appear.MST/1216

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.24

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effect of interrupted accelerated cooling, in the range from finish rolling temperature to 600°C at rates up to 17 K s−1, on the mechanical properties and structure of V and Ti microalloyed steel bars was investigated. The influence of reheating temperature, in the range 1000–1250°C, and finish rolling temperature (starting cooling temperature), in the range 800–1000°C, was also studied. Interrupted accelerated cooling caused a double enhancement of grain refinement and an increase of precipitation strengthening resulting in increases of yield strength up to 750 MN m−2and elongations greater than 25%. Increasing the reheating temperature to 1100 and 1250°C for V and Ti steels, respectively, enhanced the increment of precipitation strengthening due to accelerated cooling, but had no effect on grain refinement. Interrupted accelerated cooling was found to be most effective for improving yield strength when it is started at higher temperatures in theγregion. Accelerated cooling effectively inhibited bainite formation and produced very fine grain size at high finish rolling temperatures. This technique is therefore very attractive for processing of microalloyed steels because of the possibility of attaining very fine grains without decreasing the finish rolling temperature, thus reducing the process time.MST/1180

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.28

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effect of temperatures between ambient and 150°C on the critical strain at the onset of wrinkling in aluminium sheet deformed in a strip drawing test and on the rate of growth of wrinkles has been investigated. It was confirmed that the delay in the onset of wrinkling and in the growth of wrinkles is a result of the decrease in the compressive component of the surface stresses as the temperature increases. The correlation between the decrease in elastic modulus and yield strength and the increase in the work hardening exponent and coefficients of normal plastic anisotropy, similar to that observed at room temperature, can be attributed to the effect of temperature on these properties.MST/1245

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.37

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA metallurgical evaluation of the weldability of a high pressure/intermediate pressure turbine rotor has been undertaken to determine whether AS1M A470 (class 8) rotors can be weld repaired. The work was carried out using a retired rotor that had been in service for over 20 years. The rotor base material was found to have experienced embrittlement during service. It was determined that no heat treatment was necessary before welding, as long as a post-weld heat treatment at 677°C was performed. The coarse grained bainitic structure and embrittled condition of the rotor material were metallurgical factors for possible reheat cracking of the heat affected zone (HAZ) in this type of rotor. However, the grain refinement experienced by the HAZ and the coarsening of carbides in the coarse grain HAZ improved the toughness greatly and eliminated or reduced the susceptibility of reheat cracking. The weldment produced shows good room temperature mechanical properties; however, the stress rupture properties of the HAZ could not be evaluated owing to the premature failure of the weld metal.MST/822

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.42

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA series of laser and gas tungsten arc welds traversing stainless steels of different chemical compositions has been studied, to elucidate the role of austenite or ferrite nucleation and cooling rate on solidification behaviour. It has been found that a steel with a high CrEQ/NiEQratio can be induced to solidify as metastable austenite by initiating the weld in a steel with a lower CrEQ/NiEQratio in which the thermodynamically stable solidification mode is austenitic. The austenite dendrites are then found to continue growth across the weld junction into the undiluted regions of the high CrEQ/NiEQratio material. By providing austenite particles in this way, nucleation is rendered unnecessary and it is found that solidification to metastable austenite can be induced at cooling rates significantly lower than previously encountered. The results of these and other experiments in which the welding speed was changed during the experiment are interpreted to yield new information about the mechanisms of solidification and transformation in stainless steels during welding under conditions consistent with high cooling rates.MST/1240

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.50

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe fine grained, equiaxed duplexα/βphase microstructure of Ti–6AI–4V alloy enables large uniform plastic strains to be obtained under superplastic conditions. In this paper the role of microstructure and texture in superplastic deformation is considered. A banded, two phase microstructure gives rise to anisotropic superplastic flow stresses and strains, and can affect post-formed mechanical properties. The effect of microstructure is discussed with reference to the behaviour of Ti–6AI–4V alloy in various product forms: thick and thin sheet, extruded section and tube, and rolled bar. Manufacturing costs may dictate the use of fusion welding or diffusion bonding before superplastic forming, and the effect of such joints on deformation is described. The above data are related to other published work on Ti alloys, and the implications for the manufacture of components by superplastic forming are considered.MST/1328

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.1.62

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor