摘要:

AbstractSome aspects of the research into hot isostatic pressing currently being undertaken at Cranfield are reviewed. The advantages of this process as applied to a wide range of materials, including metals, ceramics, polymers, and their composites, and the potential development of novel materials by combining the technique with other processes, particularly surface engineering, are discussed.MST/1713

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.753

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractIt was found that on annealing supersaturated and cold rolled Al–4Cu at 280°C subgrains were initially formed as a result of the rearrangement of dislocations. Concurrent with the formation of subgrains having well defined boundaries,θparticles were formed, situated mostly on the subgrain boundaries, and the growth of subgrains was therefore severely hindered by the particles, leading to continuous recrystallisation for annealing times up to 10 000 min at 280°C. The pinning force due to particles located on the subgrain boundaries was much greater than that due to randomly dispersed particles. Subgrain growth was found to be arrested for particle parameters f/r of greater than 0·25μm−1, where f is the particle volume fraction and r is the mean particle radius.MST/1572

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.760

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractTo investigate the effect of microstructural evolution during heat treatment in newly developed Cr–2W ferritic steels containing from 2 to 15%Cr, Charpy impact testing was carried out after quenching, tempering, and subsequent prolonged aging at 873 K for 3600 ks (1000 h). The ductile to brittle transition temperature (DBTT) and the upper shelf energy were determined as functions of heat treatment and Cr concentration. The fracture sequence was examined on fractographs obtained using scanning electron microscopy. The steels consisted of bainite, martensite, andδferrite phases and carbide precipitates, depending on the Cr concentration. The DBTT decreased considerably after tempering compared with after quenching, but increased again somewhat after subsequent prolonged aging. The upper shelf energy exhibited converse behaviour. Concerning the effect of alloy phases, the DBTT was increased significantly by the formation ofδferrite and was slightly higher for the martensite than for the bainite. The effects of the alloy phases and heat treatments on the DBTT are discussed by considering the microstructural evolution, such as dislocation recovery and carbide precipitation, during heat treatment.MST/1573

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.763

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractHardness H, interjlake spacingλ, and tensile properties are reported for Al–12·7Si and Al–12·7Si–0·2Sb (all wt-%) eutectic alloys directionally solidified at growth velocities of up to 250μm s−1and under temperature gradients in the liquid of up to 12·9 K mm−1. The hardness is related to interflake spacing by the equation H=Ho+Kλ−0·2, where Hois the initial hardness of the alloy. This behaviour contradicts previous results, which suggest that a Hall–Petch relationship is followed. The tensile properties are shown to follow similar behaviour, confirming that hardness shows the same dependence as proof stress on interflake spacing. However, the nature of the relationship depends on the Si morphology and caution should be exercised in using hardness or interflake spacing to indicate proof stress.MST/1585

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.764

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe microstructure and distribution of alloying elements in a hot rolled, low alloy plate steel containing (wt-%) 0·15%C, 0·26%Si, l·49%Mn, and 0·03%Al were examined using light microscopy and electron probe microanalysis. Microstructural banding was caused by microchemical banding of manganese, where alternate bands of proeutectoid ferrite and pearlite were located in solute lean and solute rich regions, respectively. Bands were well defined for a cooling rate of 0·1 K s−1, but banding was much less intense after cooling at 1 K s−1. At a cooling rate of 0·1 K s−1and for austenite grains smaller than the microchemical band spacing, austenite decomposition occurred via the formation of‘slabs’of proeutectoid ferrite in manganese lean regions resulting in the growth of ferrite grains across austenite grain boundaries. Abnormally large austenite grains result in the formation of large, irregularly etching pearlite nodules which traversed several bands. In specimens cooled at 1 K s−1, ferrite/pearlite banding did not exist in regions where austenite grains were two or more times larger than the microchemical band spacing.MST/1397

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.777

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractIn the present work the relationship between the microstructure and the hardness of an AISI H-13 tool steel both with and without an addition of niobium was studied. Extensive investigation by direct observation using optical and electron microscopy was carried out. It was found that the deformation during ausforming introduces changes in the microstructure, such as high dislocation density and carbide precipitation, which affect the hardness of the steels. The results show that the partial substitution of vanadium by niobium does not lead to any significant change in the hardness of the hot work tool steels investigated.MST/1559

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.785

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractStudies of isostatic diffusion bonding of microduplex stainless steel have been made for two surface finishes at temperatures in the range 1200–1320 K for times of up to 10 h and pressures of up to 2·8 MPa. Bond quality has been assessed using metallography, compressive lap shear testing, and scanning electron microscopy of the fracture faces of lap shear testpieces. Sound bonds were observed with recrystallisation across the bondline for a range of conditions, although it was always possible to detect the mterface because of the presence of small oxide particles. Bonding at temperatures<1273 K led to hardening and embrittlement of the steel owing toσphase formation. Comparison of experimental bonding times for a pressure of 2·1 MPa with times predicted by an isostatic diffusion bonding model showed substantial discrepancies. Although the discrepancies could partly be a result of uncertainties in the material parameters used in the model, it is probable that the interfacial oxide has acted as a diffusion barrier reducing the rate of mass transfer, thereby increasing experimental bonding times.MST/1602

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.791

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe wear resistance of both laser melted and conventionally quenched 1·0%C tool steel has been investigated. From unlubricated wear tests, the abrasion resistance of laser treated material was found to be superior to that of conventionally treated material, both in the as treated condition and after a range of tempering treatments (room temperature at 300°C), as a result of the presence of retained austenite.MST/1326

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.796

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe principles of laser transformation hardening were investigated using a low alloy special steel having a microstructure of pearlite and proeutectoid ferrite. Temperature fields and phase transformations were modelled. Particular attention was paid to increases of the Ac1and Ac3transformation temperatures owing to the rapid thermal cycles produced by laser heating. Dissolution of proeutectoid ferrite is shown to control the formation of a homogeneous hardened case. Experimental data are in good agreement with the predictions of the model. A diagram was constructed which describes the case geometry and microstructure in terms of the process variables and is an aid to optimising practical processing parameters. The models are flexible and may be used for laser transformation hardening of other ferrous alloys having inhomogeneous microstructures.MST/1606

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.799

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe chevron notch testpiece geometry has been used in three and four point bending to evaluate the toughness of silicon carbide and silicon carbide reinforced with particulate titanium diboride. The toughness values obtained do not appear to depend either on initial chevron notch depth m the range 0·2≤αo≤0·4 or on chevron notch included angle in the range 40≤θ≤120°. This testpiece geometry allows relatively subtle effects of reinforcement in increasing the toughness of the monolithic material to be assessed with confidence. It also provides a convenient method of measuring toughness over a wide range of test temperatures.MST/1595

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.9.805

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor