摘要:

AbstractThe formation and evolution of the grain boundary silicate phase in a commercially available 8 mol.-%Mg partially stabilized zirconia powder during the early stages of sintering has been studied using analytical transmission electron microscopy. The results show that forsterite is the first formed silicate phase in the range 1350–1450°C. Between 1550 and 1600°C, forsterite melts incongruently to a silica-rich composition which wets tetragonal zirconia, pulling the individual grains into clusters. However, below 1700°C, the silicate does not wet the cubic zirconia grain boundaries significantly. The consequences of this behaviour on the sintering of the ceramic are discussed.MST/559

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.321

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe activity of N inα-Fe is derived from the solubility at fairly low temperature (580°C) in the Fe–N diagram. The interaction coefficients between Fe and N, Fe and C, and C and N are obtained and the phase boundaries of single-phaseɛ- andγ′-fields are subsequently calculated. The calculated results show that theγ′-region of the Naumann and Langenscheid Fe–C–N ternary phase diagram is correct, but theɛ-region requires revision. The calculations suggest that recent experimental data on theɛ-phase appear reasonable. Calculations taking graphite to be a standard state confirm this conclusion.MST/385

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.325

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe high-temperature mechanical behaviour of copper, Cu–Al alloys, and nickel has been examined using torsional testing with hollow testpieces in conjunction with microstructural observations on deformed and quenched specimens using both optical and electron microscopy. Dynamic recrystallization occurred in these materials as the restoration process during high-temperature deformation. The factors influencing dynamic recrystallization have been considered, including materials of high stacking fault energy. It was found that the regime of dynamic recrystallization and the transition in flow stress behaviour could be reasonably represented in terms of the Zener–Hollomon parameter. In Cu–Al solid solution alloys, although the addition of the solute aluminium into copper lowered the stacking fault energy, dynamic recrystallization was retarded to higher strains due to the reduced mobility of the grain boundary. By mechanical and microstructural analysis of the behaviour of various single phase metals and alloys during dynamic recrystallization, the factors influencing the behaviour (i.e. stacking fault energy (solute elements), Zener–Hollomon parameter (deformation condition), and strain) can be summarized on a three dimensional schematic.MST/587

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.329

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractReverse-torsion fatigue tests on Cu–10Ni alloys containing small quantities of iron in 1 atm gaseous hydrogen, oxygen, and humid air environments, showed that the fatigue life was significantly influenced by the test environment. Multiple crack initiation, crack branching, and changes in fracture mode were observed in the aggressive environments when compared with tests conducted in dry helium. The results are rationalized by a softening mechanism promoted by either hydrogen-assisted overaging or oxidation of the iron particles leading to subsequent decohesion of interfaces in the deformation zones ahead of the crack front.MST/585

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.338

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractExperiments designed to investigate the corrosion resistance of several lithium-containing aluminium alloys are described. Intergranular corrosion was investigated using the NAWL test, exfoliation corrosion using the EXCO test, and stress corrosion using the C-ring test. It was found that intergranular corrosion varied with extrusion parameters and was more severe in copper-containing alloys. Alloys containing less than 0·4% Cu were not susceptible to stress corrosion. In alloys that failed, susceptibility increased as the aging treatment was extended from the underaged to the peak aged temper and also with increasing copper content. The addition of copper to ternary Al–Mg–Li alloys also increased the exfoliation corrosion attack.MST/494

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.345

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractSolid state (diffusion) bonds have been developed in AA 7475E sheet material using different regimes of bonding temperature, pressure, and time. The bonds produced have exhibited shear strengths in the range 30–150 MN m−2and have been found to be capable of withstanding peel during a slow high-temperature superplastic forming operation. However, the bonds formed under any one set of bonding conditions showed an extremely wide variation in both shear strength and shear fracture mode. The source of this wide variation has not yet been identified.MST/601

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.353

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractMicrostructure maps were constructed for a C–Mn steel and microalloyed steels of the same base composition, after intercritical annealing to produce 23 and 50% of austenite. The critical cooling rates for the transformation to martensite of 90 and 50% of the austenite present were thus determined as functions of the carbon content of the austenite. At the 90% martensite level, the hardenability of the austenite was very similar to that of fully austenitized steel of the same composition, and varied identically with carbon content. At the 50% martensite level, the hardenability of the austenite was considerably greater than that of fully austenitized steel of the same composition. The presence of niobium and vanadium had no effect on the martensitic hardenability of the austenites: by forming carbides they simply altered the carbon content of the austenite at a fixed volume fraction of austenite. It is proposed that the martensitic hardenability of austenite of dual-phase steel depends on the size of the austenite volumes as well as on their carbon content. In the present study, the size of the austenite volumes was large enough to make them more hardenable than would be predicted on the basis of standard hardenability data for fully austenitized steels.MST/548

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.360

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractPrediction of transformation kinetics in steel at varying temperature is of great practical importance in different areas of heat treatment and material science. By formal generalization of the conventional isothermal kinetic functions applied for characterizing thermally activated processes, new types of kinetic function were generated which are suitable for the phenomenological description of non-isothermal processes. On the basis of these generalized kinetic functions, various numerical quantities allowing the concise characterization of the processes taking place at varying temperature may be derived. These quantities involve equivalent time and temperature and extended variants of well known complex time–temperature parameters (e.g. Hollomon–Jaffe parameter). With the help of these quantities, non-isothermal processes may be compared using numerical criteria. Application of the method suggested in the field of heat treatment is demonstrated by two examples. One is related to the prediction of hardness decrease due to tempering in a hardened steel, while the other concerns the development of a new type of tempering chart which can be applied generally for determining the required tempering parameters.MST/496

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.365

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe investigation was carried out on several laboratory steels with various contents of carbon, manganese, aluminium, and sulphur. The samples were cast in a metallic mould, stripped at ~1300°C, and subjected to various heat treatments. The influence of manganese, carbon, and aluminium on sulphur solubility at solidification was determined by direct electron probe microanalysis. The temperature at which the cooling from solidification was interrupted has virtually no influence on the size of intergranular particles. The size of particles depends on the content of manganese, carbon, and aluminium in steel, while a prolonged isothermal annealing has a very limited effect. Intergranular particles are smaller in steel with transformation structure than in steel with solidification structure. No gradient of sulphur was found in grain boundary areas, it is concluded that intergranular particles do not originate from sulphur in solid solution in the interior of solidification grains.MST/589

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.372

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe wettability of SiC by pure aluminium and aluminium alloys has been measured using the dip coverage method. It was found that alloying elements such as silicon, manganese, iron, and elements of the IVA, VA, and VI groups improved wettability by decreasing the incubation period and/or increasing the wetting rate. It was possible to analyse, the wetting process by assuming that the wetting rate was proportional to the amount of nuclei on the interface and to the unwetted area. The values of overall reaction rate constant koand incubation periodτobtained from this theoretical analysis had a periodic relation to the atomic number of the element.MST/561

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.5.378

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor