摘要:

AbstractIndentation tests are well established methods of measuring the hardness and toughness of surfaces, and the results can often be related to wear behaviour. Response to indentation in simple tests has been used in models for sliding wear, abrasion, and impact erosion; more sophisticated procedures can provide additional information about wear by stress corrosion. Despite the increased refinement of indentation fracture models, the scope for assessing the accuracy of theoretical predictions is limited considerably by the approximations used in the theories and the poor reproducibility of wear test data. An aspect of wear usually neglected is the brittle failure of edges and corners of components and tools. Recently, many of the experimental problems associated with using indentation to measure the susceptibility to edge flaking have been overcome, and it may soon be possible to recommend a test procedure for measuring this property.MST/452

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.641

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe effect of post-curing on the moisture absorption characteristics of Fibredux 914/T300 carbon fibre–epoxy composites, and hence on their thermomechanical behaviour, has been examined. Laminates 1 mm thick were post-cured at 190 or 210°C for 4 or 10 h. The various cross-link densities thus established had almost no effect on the moisture absorption behaviour. Interlaminar shear strength and torsion pendulum tests gave similar results, in that the cross-link density had almost no influence on the dynamic shear modulus or the mechanical dissipation factor. From these findings, environmental degradation of the composite is shown to depend on the content of absorbed water. The behaviour of the composite in hot, humid conditions therefore cannot be improved by post-curing treatment.MST/400

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.647

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractAn evaluation of the C–W system has been made using a two–sublattice regular solution model for the interstitial solution phases and an ordinary subregular solution model for the liquid phase. A set of parameter values describing the Gibbs energy of each individual phase is given.MST/275

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.653

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe transient behaviour of dynamically recrystallizing nickel following a change in strain rate has been studied using hot tensile testing, with microstructural observations being carried out by optical and transmission electron microscopy. After a decrease in strain rate, the flow curve displayed multiple peaks accompanied by grain coarsening, whereas after an increase in strain rate, the flow curve displayed a single peak associated with grain refinement. Grain coarsening after a strain rate decrease occurred in three distinct stages, in contrast to the monotonous grain refinement taking place after a strain rate increase. In the first stage, rapid grain boundary migration caused a sharp drop in flow stress over a strain of 0·002. In the second, the new grains grew, causing coarsening and impingement, with rapid work hardening in the softer regions. Finally, in the third stage, the grain size increased further, approaching the steady state value, while multiple peaks in flow stress were observed.MST/372

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.659

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractCleavage fracture of a 26Cr–1Mo ferritic stainless steel has been studied using fatigue precracked specimens. The parameters determined were fracture toughness, cleavage fracture strength, and effective surface energy of ferrite. The results have been compared with earlier results on notched specimens.MST/185

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.666

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractHot ductility, measured by reduction in area, has been determined over the temperature range 550–950°C for a series of plain C–Mn steels having the same base composition except for the carbon content, which was in the range 0·04–0·65 wt-%. A ductility trough was obtained for all the steels and minimum ductility values were similar. Raising the carbon content from 0·04 to 0·28 wt–% caused the ductility trough to move to lower temperatures and this was in agreement with the observed changes in transformation temperature. Tensile fracture at the minimum ductility temperature was along thin films of ferrite which formed round the austenite grains–generally by deformation–induced transformation. The softer ferrite allowed strain concentration to cause ductile voiding at the MnS inclusions, and the voids eventually linked up to give intergranular failure. Raising the carbon content above the 0·28% level caused a change in the fracture mode. Instead of the ductility troughs moving to lower temperatures, a shift of over 100 K to higher temperatures was observed. Intergranular failure now occurred in the austenite as a result of grain boundary sliding. It is suggested that this change in fracture mode is caused by carbon increasing the activation energy, and hence the critical strain required for dynamic recrystallization, so favouring the linking of cracks formed by grain boundary sliding.MST/366

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.671

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractMany high–temperature creep tests are performed on low–chromium, ferritic steels in an uncontrolled atmosphere. Examination of creep rupture specimens of 0·5Cr–0·5Mo–0·25V steel tested in air has shown that decarburization accompanies oxidation and is an important factor in accelerating the failure of creep tests in air. Similarly, pre-aging in air reduces the creep life more than pre-aging in a capsule. There is also evidence that decarburization is accelerated during straining. Measurements of surface carbon contents in 10 mm thick blocks heat treated in air at 600–700°C have given an apparent activation energy for decarburization of about 250 kJ mol−1, at least twice that for carbon diffusing in ferrite. However, this value is still below that for creep, so the influence of decarburization on creep life is expected to increase at lower temperatures. Structural observations are discussed in relation to loss of carbon and are related to creep behaviour. Secondary precipitation was observed after low-temperature treatments in aged encapsulated specimens, but not in specimens aged in air. This is attributed to the loss of carbon in the air aged specimens, which also showed a decrease in the M3C content. The iron content of M3C particles depends on carbon content as well as aging time.MST/40

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.677

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThree superheater transition joints, between 2·25Cr–1 Mo and 316 stainless steel, welded with nickel–base weld metal, removed from service after 72337 h, have been examined using optical and scanning electron microscopy. In addition, microhardness measurements have been made and local chemical compositions have been analysed using the energy dispersive X-ray attachment on a scanning electron microscope. Temperature accelerated creep rupture tests have been carried out between 590 and 625°C at stresses of 31–62 MN m−2on cross–weld tensile specimens machined longitudinally from the walls of the joints. Detailed metallographic examinations showed the same failure mode as that found in long–term service failures. Therefore, the use of post-exposure temperature accelerated testing of uniaxial cross-weld specimens appears to be a viable method of assessing the remanent life of nickel-base transition joints operating at elevated temperatures. The applicability of various multiaxial stress rupture equations to transition joint failures is considered. The present rupture data are compared with previous data generated from initially as-welded specimens to provide upper and lower estimates of the long-term failure lives.MST/403

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.686

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe mechanism of roping in two ferritic stainless steels (type 18·2 and type 430) has been studied. The effects of structure, substructure, and texture are considered in relation to hot and cold process parameters and results obtained from deep drawn cups and tensile specimens. The mechanism of roping is shown to result from differential yielding under tension, caused by heterogeneous bands of material which are developed during the hot rolling schedule. It is shown that small dispersions of austenite can prevent this banding effect.MST/335

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.693

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractA range of sialon compositions have been used to machine the nickel-base alloy Incoloy 901. Wear measurements, taken throughout the machining tests, have shown that tool life and flank wear resistance increase withα-sialon content. An examination of the wear mechanisms involved suggests that this can be ascribed to the increased resistance to dissolution into the work piece, afforded by the higher aluminium and oxygen levels inα-sialon compared with those inβ–sialon. At higher cutting speeds one of the main mechanisms of tool wear was rake face flaking, and resistance to this mechanism was found to increase with tool material grain size. A model has been proposed for the initiation and propagation of the cracks which produce this type of failure. At lower cutting speeds depth-of-cut notch wear was of major importance, and resistance to this mechanism was found to decrease with increasing grain size.MST/249

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.7.700

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor