摘要:

AbstractThe methods for producing magnesium are briefly described and its alloying behaviour is discussed with particular reference to the roles of individual alloying elements. Cast and wrought alloys are considered separately and particular attention is paid to microstructure–property relationships and corrosion behaviour. Alloys produced via new processing techniques are treated separately and mention is made of metal matrix composites and the use of rapid solidification to produce amorphous and other novel materials. Finally, current and future trends in the use of magnesium alloys are considered together with examples of recent applications.MST/2023

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.1

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractUnidirectional solidification has been employed to cast Ti–Al specimens containing TiAl lamellae separated by narrow Ti3Al lamellae. These lamellae were parallel and continuous throughout the specimens. Two different compositions, Ti–49·1 at.-%Al and Ti–50·8 at.-%Al, were used since the differing compositions resulted in different spacing between the lamellae, the latter displaying a wider spacing. Specimens were rolled with the plane of the lamellae parallel to and at 45°to the rolling plane in order to assess how ductility is affected by lamellar spacing and the direction of slip relative to the lamellae. Deformation was found to be highly anisotropic; ductility being greater when slip occurred in a direction parallel to the lamellae than when slip occurred in a direction at 45°to the lamellae. Reducing the width of the lamellae resulted in an improvement in ductility in both easy and difficult slip directions and this has been attributed to a reduction in the concentration of stress at lamellar boundaries.MST/1869

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.17

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractGuided by the results and concepts of band theory and tight binding theory, a simple model of cohesion in TiCxand related compounds is proposed, in which each carbon atom claims four d electrons from its transition metal neighbours to form saturated covalent bonds; and in which any d electrons surplus to this are used to form metal–metal covalent bonds. In the non-stoichiometric alloys, the atomic heterogeneity of the structure plays a significant secondary role in allowing carbon free octahedral cells to expand slightly and therefore increase the overall lattice constant. Using cohesive parameters derived from experiment, this model is able to represent approximately the observed variation of lattice constant with composition and the range of existence of the TiCxphase.MST/1876

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.22

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractWhen oxidised at 973 K, annealed 9Cr–1Mo steel forms convex oxide ridges at the boundaries of prior austenite grains. In addition to this morphological difference these grain boundary oxides show compositional dissimilarities with the oxides formed within the grains, as suggested by the results of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) , and substantiated by secondary ion mass spectrometry (SIMS) results. Both EDX and secondary ion imaging confirm the high Si content of the oxides in the ridges. However, it is the synergistic influence of the variations in the chemical composition and morphological features of scales that governs the stability of the oxides growing within the alloy grains. These variations have their origin in the oxidation process at the alloy grain boundaries. Hence, to achieve a more complete understanding of this phenomenon, oxide ridges and the scales within the grains have been extensively characterised by obtaining depth profiles using SIMS and observing the morphological evolution using SEM and surface profilometry. The oxide ridges act as discontinuous interfaces, so that the oxides growing in the adjoining areas experience sufficiently high stresses to produce spalling. The finer the alloy grains, the greater the number of discontinuous interfaces (i.e., grain boundary ridges) and the stressed area, and therefore the earlier spalling occurs.MST/1824

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.27

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractMeasurements of 0·2% proof stress, ultimate tensile strength, elongation, and impact energy are presented for low Mn, Cu and low Mn, Ni–Cu irons for various austempering conditions and related quantitatively to microstructural features. It is shown that the formation of more than 20% pearlite in the austempered structure causes an unacceptable reduction in mechanical properties. The pearlite affects ductility in upper bainitic irons and strength in lower bainitic irons. The 0·2% proof stress is shown to be dependent on the bainitic ferrite particle size and a Hall–Petch relationship exists between proof stress and particle size. The impact energy of irons austempered within the processing window is shown to increase with increasing volume fraction of retained austenite and then to reach a saturation level. The saturation level is discussed in terms of the occurrence of a transformation induced plasticity mechanism.MST/1900

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.35

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThree Hadfield manganese steels were investigated containing 1·15, 1·40, and 1·70 wt-%C, all with about 13 wt-%Mn. The as processed steels consisted of austenite grains, 10–12μm in size, with a dispersion of carbides. The steels were deformed at temperatures in the range 500–950°C in three different phase regions, namely, three phase (austenite + carbide + ferrite), two phase (austenite + carbide), and single phase (austenite). Ultrafine microstructures were developed during large strain torsional deformation. The large torsional deformation in the two phase region resulted in grain refinement through dynamic recrystallisation with the austenite grains pinned by carbide particles, minimising grain growth. Strain assisted transformation followed by spheroidisation of carbides was obtained on testing in the three phase region. The concurrent deformation and transformation resulted in ultrafine microstructures of submicrometre size constituents. Torsional properties were evaluated and related to the observed microstructural changes. Stress exponents of about 7 were obtained. The activation energy for the deformation process was found to be close to that for lattice self diffusion of iron in austenite.MST/1843

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.41

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe addition of Co to 18%Ni maraging steels produces an increase in hardness due to a synergistic effect. A similar effect is reported in this paper for maraging steels based on Fe–5Mn–6Ni. However, Co is thought to have an effect on the ductile-brittle transition temperature (DBTT) of mar aging steels. The addition of 9%Co to the base alloy plus 2·5%Mo increases the DBTT to 120°C in unaged material. Similar to reports by other workers on Fe–Co alloys, it is considered that this increase in DBTT is due to Co restricting cross-slip. In contrast, Mo is thought to lower the DBTT by increasing cross-slip. The reason for 2·5%Mo changing the mode of brittle fracture from intergranular to transgranular cleavage in the base alloy is discussed. Mention is also made of the effect of Ni on the DBTT in lath martensite structures. In classical 18%Ni maraging steel, the DBTT of the Fe–18Ni base is probably so low that the addition of Co does not seriously embrittle the steel.MST/1828

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.52

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractLaser beam welding of 13 mm plates of HY 80 steel resulted in different microstructures in the fusion zone depending on the welding process. Autogenous welds resulted in an untempered martensitic structure, whereas, with the introduction of a hot wire filler metal, the microstructures depended on the wire feed. A slow feed resulted in a mixed martensite–bainite microstructure and a fast wire feed resulted in a microstructure that is primarily acicular ferrite. The chemistry of the as deposited weld metals was different in each case. The thermal profiles for the autogenous weldment were calculated based on a two parameter model of laser welding that utilises the fusion zone boundary as a measure of‘best fit’. Based on the cooling rate of the autogenous fusion zone, cooling rates for the two welds with hot wire filler metal were rationalised. Using these cooling rates, the chemistry of the weld metal and a model of microstructural development of the weld metal, a computer calculation was made which gave volume fractions of the phases similar to those observed experimentally.MST/1845

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.56

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe microstructures of titanium aluminide based composites have been investigated using optical microscopy, scanning electron microscopy, energy dispersive spectrometry, transmission electron microscopy, and scanning transmission electron microscopy. The composites were in the form of pellets of ~3 mm dia. produced by laser melting various mixtures of titanium, aluminium, and silicon carbide using 800 W laser power, 3 mm beam diameter, and 0·5 s pulse time. In all the processed samples, titanium and aluminium were completely melted and formed an alloy, whereas, SiC particles were partially dissolved leading to the enrichment of the alloy matrix with silicon and carbon. The aluminium contents of the matrixes of the composites spanned the range from ~15 to ~78 at.-%. In the 15–42 at.-%Al range, the phases formed during solidification wereβtitanium solid solution, TiC, and Ti5(Si,Al)3;βand Ti5Si,Al)3occurred together as a eutectic constituent. During solid state cooling,βphase transformed to either martensite or anα2+γmixture, depending on the aluminium content of the matrix. At 57 at.-%Al the matrix solidified to formγ, TiC, and Ti5(Si,Al)3. The composite with 78 at.-%Al contained dendrites of Ti(Al,Si)3and interdendritic aluminium solid solution. Features of the Ti–Al–Si–C phase diagram are discussed in relation to the microstructures.MST/1841

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.60

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractSurface transformation hardening of several Cr–Mo steels, namely, AISI 4140, 4130, and 4118, was carried out using a CO2laser. The influence of processing variables and tempering conditions of the specimens on the case depth Zcof laser hardened zones was analysed. The ease of formation of a hardened layer in tempered steels during laser treatment was represented by a parameter M, which is simply a function of the specimen hardness. An empirical equation was developed to describe quantitatively the superheating effect in the laser hardening process. The superheating∆T above Ac3was then related to the M value for the specimen and the heating rate in the laser treating process. Using the experimental results of the as quenched specimen as calibrated standards, Zcversus M curves could be constructed for each steel. These diagrams are useful in predicting the case depth of tempered steels in the laser hardening process.MST/1834

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.1.69

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor