摘要:

Magnesium based Mg-9Al-lZn-5RE (RE = La or Nd) alloys were rapidly solidified by chill block melt spinning. The resulting ribbons were cold packed into an aluminium alloy can and extruded at temperatures of 230 and 340°C and ratios of 20:1 or 25:1. Tensile and hardness tests of the extruded and heat treated materials were carried out. The tensile strength and elongation to fracture of the as extruded material were 478 MN m−2and 6·5% respectively and those of the material heat treated for 2 h at 350°C were 420 MN m−2and 20% respectively. The microstructure of these specimens was studied by X-ray diffraction and transmission electron microscopy. Intermetallics of Al11La3or Al2Nd were found at grain boundaries and in the matrix which had a grain size of between 0–26 and 0–8μm, while Mg17Al12precipitates were present in the specimens extruded at a lower temperature (230°C). Yield strengths were consistent with the Hall-Petch relationship with grain size established earlier for this class of material.MST/3495

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665711

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The solubility of copper in titanium carbide (TiCx) was studied experimentally. The solubility was assessed in two different ways: (a) titanium carbide was added to a copper—titanium melt, (b) titanium carbides formed in situ, from graphite and titanium, were analysed. The stoichiometries were implicitly assessed. The solubility of copper in titanium carbide was found to decrease with increasing carbon content. This behaviour was compared to the solubility of chromium in titanium carbide, which increases in solubility with increasing carbon content. The role of vacancies in the solution is briefly discussed.MST/3502

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665712

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Several methods have been developed recently for semiautomatic or automatic microstructure characterisation. In general, they are limited in their ability to distinguish accurately the regions or objects of interest. This can be critical in ceramography where features are not easily separated with respect to the matrix. A versatile and highly efficient technique using the Khoros system, a powerful image processing environment, is presented for microstructure morphological characterisation. The technique implemented is essentially based in the boundary reconstruction of the features that are not well delineated. The method allows image contrast to be improved, image defects to be corrected, morphological features to be extracted, and parameters for microstructure characterisation to be determined. To illustrate the performance of this technique, several morphological parameters of grains and precipitates in compact hydroxyapatite are determined.MST/3443

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665713

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Bimaterial laminates may produce enhanced fracture resistance in brittle and semibrittle materials. The purpose of the present work was to investigate crack stabilisation in a discontinuously reinforced aluminium (DRA) material via lamination with a ductile aluminium alloy. In particular, the crack growth behaviour of the individual DRA layers in the laminate was compared with that of an equivalent thickness DRA material tested separately. In contrast to the DRA material, the DRA laminate exhibited R curve behaviour in which stable crack growth occurred concurrent with an increased load carrying capacity after fracture initiation, producing both an increase in the toughness and the work of rupture.MST/3520

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665714

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Room temperature fatigue tests in the form of four point bending were performed at a frequency of 20 Hz and a load ratio R= +0·1 on electropolished Waspaloy specimens taken from a forged turbine disc. Samples, which had a partially recrystallised microstructure with a bimodal grain size, were removed from the outer rim of the disc. The S-N curve was similar to that reported for a fully recrystallised structure with a coarse grain size, from the same turbine disc. The dominant crack initiation sites were found to be inclusions with a subsequent stage I crack growth generally along slip bands. Other crack initiation sites observed included slip bands, annealing twins, and grain boundaries. Fatigue deformation occurred by the propagation of planar slip bands. Slip band cracks formed more frequently in coarse grains than expected from their volume fraction. Fluctuations in short crack growth rate were observed and were associated with microstructural features such as grain boundaries and twin boundaries, both of which acted as barriers in the early stages of crack growth. The short crack growth rate versus stress intensity range graph was similar to those from uniform fine grained Waspaloy.MST/3413

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665715

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

High temperature tensile tests were carried out on L12type Co3Ti alloys, both undoped and doped with 1–4 at.-%Fe. There were anomalous increases of the 0·2% yield stress (yield strength) with increasing test temperature from 473 to 1073 K (or 1173 K, depending on the composition). The elongation and ultimate tensile stress (UTS) monotonically decreased with increasing temperature. The fracture surfaces of specimens showed a variety of fracture modes which were dependent on the test temperature and composition. There was a correlation between the ductility and the fracture mode: the more transgranular the fracture mode, the higher the ductility. It was found that Co3Ti with 2 at.-%Fe exhibited improved ductility and it exhibited the highest peak value of yield strength and peak temperature. The alloys were also hydrogen charged to investigate their hydrogen embrittlement behaviour. Room temperature tests indicated that the addition of 2 at.-%Fe decreased the hydrogen related embrittlement.MST/3479

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665716

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

X-ray diffraction, optical microscopy, and hardness measurements were used to determine the austempering kinetics of an alloyed ductile iron of composition (wt-%) Fe-3·49C-2·33Si-0·42Mn-0·25Cu-0·23Mo-0·035Mg at austempering temperatures of 300, 350, 375, and 400°C and austenitising temperatures of 870 and 920°C. The stage I reaction during austempering occurs in two steps, the first in the eutectic cell and the second in the intercellular area. Decreasing the austenitising temperature is shown to increase the driving force for the stage I reaction but to have a lesser effect on the stage II reaction. Decreasing the austenitising temperature produces a more uniform austempered microstructure and reduces the amount of martensite in this structure. These changes move the processing window to shorter austempering times and increase the temperature at which the processing window closes.MST/3390

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665717

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Microstructural characterisation and room temperature tensile testing were performed on a series of tungsten heavy alloys extruded at various temperatures. Ultimate tensile strength of the alloys increased with increasing extrusion ratio and with decreasing extrusion temperature down to 600°C. Fracture surface observations indicated that the tensile strength correlated with the tungsten cleavage failure mode. The matrix could inhibit the propagation of cracks initiated in the tungsten particles.MST/3384

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665718

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Fracture initiation sites were located in Mn-Mo-Ni steel specimens broken at different temperatures in the transition region. The stresses and strains at these sites were determined, and the failure probabilities calculated. The data shows that brittle fracture throughout most of the transition region can be characterised by defining a critical stressσcand a critical probability of failure at the position at whichσcis achieved. This description implies that the measured toughness transition temperature can be expected to increase with a decrease inσc, a decrease in the work to fracture, or an increase in yield stress. The variations in work to fracture with aging, proposed here to accommodate measured changes in toughness distributions, are consistent with the measured changes in phosphorus segregation with aging. The predicted proportionality between increase in yield stress and shift in transition temperature is similar to that found after irradiation.MST/3359

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665719

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The effects of three on line accelerated cooling parameters (accelerated cooling start temperature TA, cooling rateṪ, and cooling interrupt temperature T1) on transformation temperatures and microstructure in a low carbon microalloyed plate steel were studied by laboratory simulations in a quench deformation dilatometer. Varying the on line accelerated cooling parameters changes the austenite condition and transformation path. In general, the transformation path shifts from polygonal ferrite towards bainite with increasing TA, increasingṪ, and decreasing T1. There is also a corresponding refinement in the microstructure and increase in hardness. In comparison with the laboratory thermomechanical processing treatments, the multipass industrial rolling schedule produces a much more heavily deformed austenite structure than laboratory thermomechanical processing treatments, which would favour high transformation temperatures, fine polygonal ferrite microstructure, and lower hardness.MST/3425

ISSN:0267-0836    

DOI:10.1080/02670836.1996.11665720

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor