摘要:

AbstractAn elemental foil metallurgy process, based on pure titanium and aluminium foils, has been developed to produce TiAl based intermetal1ic compounds. The processing comprises five steps: coiling of pure titanium and aluminium foils, encapsulating, reaction annealing, precompacting, and hot isostatic pressing. Samples processed by this method have low oxygen contents (0·04–0·07 wt-%); a duplex layer microstructure is obtained. Foil metallurgy is shown to be an attractive processing technique to produce near net shape formed components fabricated from high quality titanium aluminides by conventional closed die forging of encapsulated Ti/Al coils before hot isostatic pressing, i.e. before the formation of the brittle TiAl.MST/2045

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.845

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA Monte Carlo computer simulation technique was employed to model the recrystallisation and subsequent grain growth of a heavily deformed metal. Seeds, from which recrystallised grains grow, were inserted in three different ways, namely, (i) uniformly, (ii) randomly over all the lattice sites, and (iii) randomly on the surfaces of grains that were present before deformation. It was assumed that all seeds were active from the start of the recrystallisation process. Various characteristics of the grains grownfrom seeds on grain surfaces were found to be very different from those of grains grown from seeds located throughout the material. In particular, the distribution of grain sizes is broader and individual grains are often elongated. By contrast, grains grown from seeds distributed throughout the material are equiaxed. However, these differences tend to be removed after recrystallisation is complete and normal grain growth occurs. The results have practical implications if the strength of the metal is of concern.MST/2035

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.855

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractIt has recently been reported that in cold rolled copper, cube oriented volumes are frequently formed in long thin bands next to bands having orientations related to the cube orientation by a 30–40°rotation about acommon pole. This microstructure would suggest that during recrystallisation, a cube oriented nucleus in the deformed structure can grow easily into its neighbour owing to the special misorientation which allows a high boundary migration rate. In this paper the formation of this special microstructural arrangement is studied by a generalised deformation banding model which involves the cooperation of two types of deformation banding. The model also predicts that the cube volumes have lower energy contents than both their immediate and bulk average surroundings. These favourable factors explain the domination of cube recrystallisation texture. In addition, the formation and implication of the cube oriented volumes surrounded by material with near {112}orientation, reported in aluminium, is also considered.MST /1994

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.862

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractInvestigations into the hardening response of 6061 and 6061–Li alloys have been carried out using analytical electron microscopy. A nucleation and precipitation mechanism has been suggested to explain the modifications of the aging behaviour of 6061 caused by the Li additions. According to this mechanism, the preferential clustering of Li and vacancies inhibits the formation of dislocation loops and diffusion of Si and Mg atoms into zones so that the precipitation of needle shaped Guinier–Preston (GP) zones is limited and delayed. As a partial replacement of the needles, AILiSi with a small lattice strain is formed through the preferential association of Li–v (where v denotes vacancies), Si–v, and AI. Consequently, a dual precipitation behaviour ofGP zones and AILiSi occurs in 6061–0·7Li, and an extremely restrained dual precipitation of this type is alsofound in 6061–2·0Li, in whichδ′is dominant. In contrast to the initial inhibition, a promotion of needle shaped GP zones is observed on prolonged aging, these being formed with the aid of defects. The inhibited nucleation and precipitation and the reduced age hardening can be improved either by increasing the Si excess or by applying two step aging.MST/1972

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.869

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe thermal oxidation susceptibility of a 30 vol.-%SiC whisker reinforced Al203composite in air at 1300–1500°C has been investigated. It was found that the morphological changes associated with scale evolution lead to the formation of mullite and a glassy phase. In particular, the scale cross-section consisted of a porous external scale (white), and an internal black layer in contact with the unreacted matrix. The black scale region was relatively thin (0–6μm), and contained partially oxidized SiC whiskers as well as glassy phases. In some .instances, the inner black scale/matrix interface exhibited intergranular cracking. The presence of these cracks was attributed to internal stresses induced by volume increases associated with the oxidation reaction. Additionally, the rates of scale thickening and of weight gain exhibited parabolic behaviour. At 1500°C parabolic rate constants Kpand Kmof 1·18×10−14m2S−1and 2·23×10−9kg2m−4S−1, respectively werefound. From the rate constant data, activation energies of 577 and 542 kJ mol−1were determined on the basis of scale thickness and weight gain, respectively. Apparently, the oxidation rates in the black subzone were somewhat high to be rate limiting. Hence, the exhibited activation energies were ascribed to the diffusion of oxidant across the white scale region.MST/2013

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.879

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractSigmafibres (SM1240) produced by a chemical vapour deposition process using a 15μm tungsten wire corefor SiC deposition have a duplex coating of graphitic carbon and TiBx. Nodules present on the fibre surface are attributed to the deposition of the carbon coating over soot particles present on the substrate. Both the carbon and TiBxcoatings were stable in vacuum or air at temperatures up to 973 K. The nodules werefound to be sites of preferential attack by the titanium alloy matrix. The average number of nodules per fibre decreased more rapidly when the specimens were heated in air than in vacuum. It is suggested that the nodules may reduce the stability temperature of the coatings.MST/2028

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.887

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe compressive behaviour of partially remelted A356 alloys reinforced with 20 vol.-%SiC particles (Duralcan F3 A20S) is investigated. The influence of isothermal holding time in the range 2–120 min in the semisolid state before compression at a constant strain rate of 0·1 S−lis investigated. It is observed that deformation always takes place under very low stresses, which decrease as holding time increases. Comparison is made with the unreiriforced alloy (A356) together with composites extruded after fabrication. The compressive behaviour in the semisolid state at various constant strain rates in the range 6·2×10−3–0·4 S−1is also investigated. Theflow stresses are sensitive to strain rate according to the classical power law (σ=K03B5;mKern, with values of m in the range 0·3–0·4. Microstructural characterisation of the specimens after partial remelting and after compression is also carried out and the correlations between the compressive behaviour and the microstructure are discussed. In particular, it is shown that the presence of the particles leads to finer, less agglomerated globules of the solid phase than in the unreiriforced alloy, which explains the high deformability of the composites.MST/1993

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.894

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractResearch has been undertaken on the microstructure, mechanical properties, and impact abrasion resistance of high manganese steels containing primary or eutectic NbC particles. The present paper presents and analyses test results on the impact deformation resistance (determined using a drop weight device) and work hardening ability of these steels. The microstructure, impact toughness, and impact abrasion resistance will be the subject of later papers. The presence of NbC particles in high manganese steel enhances its work hardening ability by reducing plastic deformation, but does not enhance the total hardness increase under identical impact conditions. The experimental results were in very good agreement with the theoretical analysis using the derived equations from the fundamental power law between the true compressive stress and true strain, and the relationship between yield strength and hardness.MST/1971

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.903

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe hydrogen embrittlement of Cr–Mo steel has been studied. The effects of tempering temperature on the hydrogen diffusivity and hydrogen assisted cracking, without external stress, are investigated. Hydrogen permeation and trapping, for the various microstructural conditions, were measured using electrochemical equipment. The microprecipitate distribution in the steel was observed using transmission electron microscopy. The steel, which was heat treated to give a variety of microstructures, was cathodically hydrogen charged and the critical microstructural sites for hydrogen induced cracking examined. Cracks initiated by the charging treatments were found to nucleate at MnS interfaces. Hydrogen diffusivity and trapping are strongly dependent on the tempering parameters.MST/1947

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.908

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe high temperature performance of dissimilar metal welds betweenferritic and austenitic materials is directly influenced by a number of material and operational factors. The welds are heterogeneous and metallurgically complex, and their performance is not well understood. The present work specifically examines the effect of slow thermal cycles on the high temperature creep behaviour of two 2·25Cr–1Mo/type 316 alloy welds: one using a type 316 filler and one using a high nickel filler metal. A third, all stainless steel weldment was also tested for comparison purposes. A vessel containing the three test welds was manufactured and strain gauges were positioned axially across the interface of each weld. This vessel was then pressurised and subjected to three different types of test cycle, each including a holding period. Twenty three separate cycles were used and the vessel was destructively examined after completion of the test period. Results indicate that the similar metal weldment exhibited behaviour typical of that expectedfor creep of a plain cylinder loaded by internal pressure. Datafrom the dissimilar weldments were different, with the creep performance affected by the mismatching properties. The observed behaviour is rationalised, with the aid of available stress analysis, based on differences in both physical and creep properties of the constituent materials.MST/1946

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.10.915

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor