摘要:

AbstractThree non-heat-treatable aluminium based materials (AA 1050, AA 1050+1%Mn, and AA 1050+1%Mg) were deformed by plane strain compression (strains of 0·5 to 2, strain rates of 0·25 to 25 s−1) at elevated temperature (300 to 500°C). The resulting microstructures and textures were studied using optical and back scattered electron microscopy and neutron diffraction. Trends in the development of the deformation microstructure and texture with deformation parameters were noted. It was found that the amount of cube texture in the deformed material decreases as the strain increases. The Zener–Hollomon parameter is not suitable for describing the evolution of cube texture during hot deformation in AA 1050. The addition of 1%Mn or 1%Mg to AA 1050 has little effect on the trends of texture development during hot working. The subgrain size in these alloys decreases with increasing Zener–Hollomon parameter, but the strain has little effect. The misorientation between neighbouring subgrains appears to be approximately independent of deformation parameters in the range of deformation conditions studied.MST/3472

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.889

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe microstructure and texture of three dilute aluminium alloys after hot deformation and annealing was assessed; In particular, the influence of deformation temperature, strain rate, and strain on the annealed texture was examined, as well as the effect of alloy composition. The microstructures of the commercially pure materials studied (Al, Al+1%Mn and Al+1%Mg) varied in the volume fraction of coarse intermetallic particles, the type of dispersoid present, and the level and type of solute in solid solution. Furthermore, the initial stages of recovery and recrystallisation were studied in detail for one of the alloys (commercially pure Al). It was found that the main recrystallisation texture component was the cube and its strength, as well as the recrystallised grain size, depended strongly on the deformation strain. The deformation strain rate and temperature, and the alloy composition also strongly influenced the grain size and cube texture strength. These results are discussed in the context of current theories for cube nucleation within cube bands in the hot deformed microstructure. The present work was carried out as part of a wider research programme, partially supported by the European Union (Brite/Euram funded), to develop micromechanical models to describe the evolution of microstructure and texture during hot deformation and annealing of aluminium alloys.MST/3376

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.897

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractModelling of radiation induced or thermal non-equilibrium segregation needs data on impurity–point defect binding energies. These data are generally unavailable although some attempts have been made to calculate them. In the present paper an approach to calculating impurity–interstitial (mixed dumbbell) binding energies is established on the basis of strain field arguments. Earlier work is slightly modified for more accurate calculation of oversized impurity–vacancy binding energies. The method is applied to predictions of various impurity–point defect binding energies in several transition metal matrixes. With the aid of these predictions, other experimental and theoretical results on impurity–point defect binding energies and radiation induced segregation are reasonably explained.MST/3512

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.904

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractTensile tests were carried out using specimens of 2009 aluminium alloy reinforced by either SiC whiskers or particles. The size distributions of the whiskers and particles in the matrix were obtained by image analysis. It was found that failure was a result of uniform void nucleation and coalescence in the as fabricated composites, or a result of fast crack propagation initiated by a flaw developed at clusters of SiC in the aged or stretched and aged composites. The strengths of the as fabricated composites were estimated based on the results of image analysis using continuum mechanics and dislocation theories. The estimation indicated that the tensile strengths are largely contributed to by composite strengthening, supplemented by residual dislocation strengthening and work hardening. Owing to the flaw controlled failure, the tensile strengths of the aged or stretched and aged composites were independent of aging time, aging temperature, and the amount of stretching. The elastic moduli of the composites were estimated using the Halpin–Tsai model and a good correlation was found between the measured and estimated moduli.MST/3438

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.911

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractAcoustic emission (AE) signals generated during the fracture and fatigue of continuous SiC fibre reinforced titanium alloy composites (SCS-6/β21S, SCS-6/Ti–6Al–4V, and SM1240/Ti–6Al–4V) have been measured, and AE parameters have been correlated with microfracture processes. The amplitude distributions of AE signals in both fracture and fatigue were found to have distinct peaks at∼90 dB with reference to 5μV at the output of the sensor used. These high amplitude AE signals were confirmed to correspond to fibre fracture by direct optical observation, and deduced from sharp crack growth rate excursions measured by an electrical potential difference method. Although the distribution of lower amplitude signals (<70 dB)changed progressively during loading to fracture, it was difficult to distinguish microfracture processes precisely since several potential fracture modes overlap in the amplitude distribution. The ratio of the peak amplitude to the rise time of the AE signals could, however, be classified into several categories, and this method of analysis is most useful in discriminating between fibre/matrix debonding events and fibre sliding events. The present work suggests that the AE technique is useful for damage evaluation in these composites, in general, and in particular it can quantify fibre fracture.MST/3352

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.917

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA method is described for obtaining mechanical property profiles for titanium alloy larninates and for titanium alloy and titanium metal matrix composite (MMC) layers composing the laminate. The properties used were bend stiffness, and bend strength and impact strength in the notched and unnotched states. A given mechanical property was normalised with respect to the titanium alloy and a property ranking ratio R1obtained which compared the same mechanical property in all the materials with that property in the basis titanium alloy. Summation of the R1ratios gave a material ranking ratio R3which provided an overall property profile for each material relative to the overall property profile for the titanium alloy and allowed a ranking of the materials. The ratio method allows rapid and effective comparisons to be made of the mechanical properties of laminates and of their component layer materials and provides a quantitative measure of the advantages and disadvantages of a laminated microstructure.MST/3481

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.923

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractX-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and electrochemical potentiodynamic experiments have been used to study the pretreatment of 2024–T3 aluminium alloy before conversion coating. The pretreatment process included vapour degreasing, alkaline cleaning and Cr based acidic deoxidising steps. This type of pretreatment is appropriate for conversion coatings which meet aerospace standards for corrosion resistance and paint adhesion. During alkaline cleaning an oxide containing Mg, Zn, Si, and Fe developed on the surface of the alloy. During deoxidation there was dissolution and etching of both the intermetallics and the basic oxide scale left after the alkaline cleaning. Characterisation by XPS indicated that the surface was coated with a thin Cr containing coating after deoxidation which provided a degree of passivation to the surface as determined by electrochemical measurements.MST/3372

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.928

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractBinary magnesium alloys containing chromium, manganese, or titanium were made using a physical vapour deposition technique. The corrosion resistance of the alloys was assessed in aqueous chloride solutions using total immersion tests in quiescent 600 mmol L−1NaCI solutions. Alloying with manganese or titanium was found to lower the corrosion rate of magnesium over most of the compositional ranges of interest, whereas addition of chromium had a detrimental effect on the corrosion resistance of magnesium. The lowest corrosion rate was recorded for a Mg–Ti alloy where the value obtained was about 80 times lower than that found for vapour deposited pure magnesium. Open circuit corrosion potential measurements conducted in 600 mmol L−1NaCl solution showed that additions of chromium, titanium, and manganese also produced deposits which were significantly more noble than pure magnesium, suggesting that these alloys would be less susceptible to galvanic corrosion.MST/3064

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.929

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe thermal embrittlement behaviour of 18Ni cobalt free (250 grade) maraging steel (T250) compared with that of 18Ni–8Co–5Mo (250 grade) maraging steel (M250) was studied for different heat treatment conditions. The effect of heat treatment was evaluated in terms of Charpy V notch impact energy. Extensive optical microscopy, TEM, SEM, and Auger electron spectroscopy established that T250 and M250 steels showed identical embrittling behaviour for all the heat treatment conditions studied. It was observed that on direct cooling from high temperatures to intermediate temperatures in the range 1073–1273 K and isothermal annealing at these temperatures, both the steels became embrittled due to the precipitation at grain boundaries of Ti(C,N) from the supersaturated solid solution of Fe–Ti–C. However, no embrittlement was observed when the steels were quenched to room temperature from high temperature treatment and subsequently reheated rapidly to the intermediate temperatures. These findings are thoroughly discussed in light of the distribution of Ti(C,N) in the prior austenite grains in the steels for the two heat treatment conditions.MST/3254

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.945

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe development of microstructure in 316L stainless steel during industrial hot forming operations including press forging (strain rate of 0·15 s−1), rolling/extrusion (strain rate of 2–8·8 s−1), and hammerforging (strain rate of 100 s−1) at different temperatures in the range 600–1200°C was studied with a view to validating the predictions of the processing map. The results showed that good correlation existed between the regimes indicated in the map and the product microstructures. The 316L stainless steel exhibited unstable flow in the form of flow localisation when hammer forged at temperatures above 900°C, rolled below 1000°C, or pressforged below 900°C. All these conditions must therefore be avoided in mechanical processing of the material. Conversely, in order to obtain defect free microstructures, ideally the material should be rolled at temperatures above 1100°C, press forged at temperatures above 1000°C, or hammer forged in the temperature range 600–900°C.MST /3469

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.11.955

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor