ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689632

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

XD™synthesis, powder blending and hot pressing techniques have been utilized to produce NiAl composites containing 4, 7.5, 15 and 25 vol% alumina whiskers and hybrid composite materials with 15 vol% Al2O3+ 10 or 20 vol%, nominally 1μm TiB2particles. The resistance to slow plastic flow was determined at 1200 and 1300 K via compression testing in air under constant velocity conditions. The stress-strain behaviour of the intermetallic composites depended on the fraction of second phases where the 4 and 7.5% Al2O2materials flowed at a nominally constant stress after about 2% deformation, while all the other composites exhibited diffuse yielding followed by strain softening. The flow stress-strain rate properties increased with volume fraction of Al2O3whiskers except for the 4 and 7.5% materials, which had similar strengths. The hybrid composite NiAl + 15Al2O3+ 10TiB2was substantially stronger than the materials simply containing alumina. Deformation in these composites can be described by the Kelly and Street model of creep in perfectly bonded, rigid, discontinuous fibre materials.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689633

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Many nickel-base superalloys exhibit creep embrittlement after exposure to oxygen-containing environments at high temperatures. This embrittlement is characterized by a region of profuse grain boundary cavitation immediately below the surface, and four mechanisms have been proposed in the literature to account for it. Since each mechanism has microstructural consequences, these have been checked metallographically. From the results given in this paper it is concluded that, for two nickel-base superalloys, cavitation is nucleated by bubbles of a gaseous internal oxide of carbon.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689634

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The effects of grain size on wedge-type crack initiation were investigated under high temperature low-cycle fatigue conditions in an austenitic 304 stainless steel at 973 K. Accumulated grain-boundary sliding (GBS) displacement and the crack initiation life were measured in fatigue tests with slow-slow and slow-fast strain wave-shapes. The accumulated GBS displacement per cycle was proportional to the grain diameter,D.Wedge-type cracks were initiated by the accumulated GBS at grain-boundary triple junctions. The crack initiation life, n1was proportional to D−0.5The grain-size dependence of n1agreed well with the analytical result that was obtained with the micromechanics model analysed by the authors.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689635

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Life predictions given by three creep-fatigue damage models, namely the‘continuous damage model’, the‘damage rate approach’and the‘time and cycle fractions summation’method, were evaluated for over 200 high temperature fatigue tests reported in the literature. These tests, which were conducted on AISI 304 and 316 stainless steels, include several different multiaxial and time-variable loading conditions (in-phase and out-of-phase biaxial stress, various strain waveforms, complex loading histories, etc.) whose influence on the distribution of the ratio between predicted and observed cycles to failure was analysed. Results obtained by the three models are discussed, emphasizing differences in accuracy and cases in which the creep-fatigue behaviour does not appear to be satisfactorily predicted.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689636

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The effects of N on the hot ductility of low carbon steels have been studied with particular emphasis on the relation with Si. The ductility of Si, Al-killed steels is largely reduced by slow strain rate (10−3–10−4S−1) deformation at temperatures from low temperatureγtoγ/αduplex phase region (from 750 to 950°C in this case), accompanied by ductile intergranular fracture of austenite. The cause of the loss of ductility is found to be dynamic precipitation of hexagonal close packed (hep) (Si, Al)N both on theγgrain boundaries and within the grains, and the phenomenon is largely enhanced by either increasing Si or N content. Similar phenomena, i.e. precipitation hardening-like behaviour and dependencies both of deformation conditions and of Si and N contents, are also observed in Al-free Si-killed steels. The cause of this ductility loss should be ascribed to dynamic precipitation of some kind of silicon nitride, although the precipitation has not been detected directly in all the specimens examined.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689637

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

An analytical study of transient heat conduction with a moving heat source/sink is considered. In this study a closed form solution is obtained. By using the solution obtained, the spatial temperature distribution and the temperature-time history could be obtained. The results obtained are compared with the numerical and experimental data presented in Part II of this work. The comparison shows that the present solution can be used to determine the effect of different heat flow parameters on the temperature pattern and history in any similar heat conduction problems.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689638

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

A theoretical and experimental study of heat flow distribution during the autogenous GTA welding of metal plates is made. The theoretical part of this study involves the development of a numerical model based on a finite-difference implicit-solution method for the transient three-dimensional heat conduction equation with a moving heat source/sink, which simulates the welding process. The experimental part of this study involves the measurement of temperature distribution in the welding workpieces. These experimental results are compared with the numerical ones and the agreement is fairly good. The numerical solution developed is easier and more accurate for studying the effect of many welding parameters on heat flow distribution, the welding speed, the input-heat energy and the type and geometry of welding workpieces.

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689639

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689640

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0960-3409    

DOI:10.1080/09603409.1991.11689641

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor