Behaviour of hydrogen in pure aluminium,Al-4 mass% Cu and Al-1 mass% Mg2Si alloys studied by tritium electron microautoradiography

The effect of lattice defects and microstructures on hydrogen distribution in pure aluminium, Al-4 mass% Cu and Al-1 mass% Mg₂Si alloys has been studied by tritium electron microautoradiography. It was found that in pure aluminium and both the alloys, dislocations and grain boundaries act as short-circuiting diffusion paths and also as trapping sites for hydrogen. It was found that the Guinier-Preston (GP) zones in the Al-1 mass% Mg₂Si alloy do not act as trapping sites but as repellants for hydrogen, in contrast to the GP zones in the Al-4 mass% Cu alloy in which they act as trapping sites for hydrogen. In the Al-1 mass% Mg₂Si alloy, the interfaces between the matrix lattice and the metastable precipitate and between the matrix lattice and the equilibrium precipitate, were proved to be strong trapping sites for hydrogen. In the Al-4 mass% Cu alloy, the equilibrium precipitate itself has been found to be able to trap hydrogen.     

Disordering of the Ni3Si intermetallic compound by mechanical milling

The ordered f c c intermetallic compound Ni₃Si was mechanically milled in a high-energy ball mill. The severe plastic deformation produced by milling induced transformations with increasing milling time as follows: ordered f c c disordered f c c nanocrystalline f c c. The structural and microstructural evolution with milling time was followed by X-ray diffraction, TEM, hardness tests, and differential scanning calorimetry (DSC). Complete disordering occurred at milling times of 2 h and kept the saturated H of the DSC peak in the range of estimated enthalpy even after 60 h milling. The structural development during milling of the f c c solid solution for Ni₃Si was presumably dominated by the formation and refinement of a dislocation cell structure into microcrystallites which eventually reached nanometre dimensions.     

原位自生Ti3 Al金属间化合物基复合材料的微观结构

采用原位自生（XD）法制备Ti3Al金属间化合物基复合材料,对复合材料的XRD,OM和SEM的分析结果表明,Ti-17Al-0.5C复合材料的基体为Ti3Al,增强相为Ti3AlC,且增强相在基体中按一定的方位排列,Ti-17Al-1.5(2.0)C复合材料的基体为Ti3Al,增强相由心部TiC矣包覆层Ti3AlC双层组成,随着含C量的增加,增强相由不发达的树脂晶变为等轴晶,对合金进行微力学探针测试表明,增强相TiC和Ti3AlC的显微硬度和弹性模量均大于基体Ti3Al,随着C含量的增加,合金中增强相和基体的显微硬度和弹性模量无明显变化。     

The synthesis of bulk material through explosive compaction for making intermetallic compound Ti5Si3 and its composites

The possibility of synthesizing Ti₅Si₃ from mixed elemental powders and the fabrication of its composites by explosive compaction is discussed. A new technique using underwater shock waves was developed and it was found to exercise better control over the influencing parameters. Two processes were employed viz., (1) direct shock-induced reaction and (2) explosive compaction followed by heat treatment. The methodology to produce bulk material by the above two processes are reported. Ti₅Si₃ intermetallic synthesized by the two processes reveals high hardness than commercially available Ti₅Si₃.     

Oxidation resistance of intermetallic compounds Al3Ti and TiAl

The oxidation kinetics and morphological features of Al₃Ti and TiAl were investigated. The oxidation resistance of Al₃Ti is much better than that of TiAl, for example, by a factor of about 30 at 1000° C for 48 h. The big difference in the oxidation resistance is related to the characteristics of the external oxide scales of a protective Al₂O₃ or a mat of crystalline TiO₂ formed on Al₃Ti or TiAl, respectively. Sufficient aluminium transport from Al₃Ti assists the formation of the Al₂O₃ scale which acts as a protective film against oxidation. The poor aluminium content of TiAl produces Ti₃Al phase at the interface of TiAl and oxide scales and increases the diffusivity of titanium in the Al₂O₃ scale. The external crystalline TiO₂ scale produced by the diffusion of titanium through the Al₂O₃ scale enhances oxidation of TiAl.     

Rapidly quenched intermetallic compounds,TiAl and Al3Ti

Two types of molten intermetallic compounds, with stoichiometric compositions TiAl and Al₃Ti, are rapidly solidified at a cooling rate ranging from 10⁴ to 10⁵ Ksec^–1 using a melt-spinning method. Solidified specimens are analysed by X-ray diffractometry and observed by a high-voltage electron microscope and an analytical transmission electron microscope. Extra phases other than stoichiometric composition phases were not detected for either TiAl or Al₃Ti specimens by X-ray diffractometry. Both specimens have very small grains from 1 to 3 m in diameter. TEM observation reveals that very fine precipitates (100 to 300 nm), which are not detected by X-ray diffractometry, are present within grains. They are Ti₃Al in the TiAl specimens, and aluminium in the Al₃Ti specimens, respectively. Electron micrographs of the Al₃Ti specimens show the presence of pair dislocations (super dislocations) and anti-phase boundaries. They are believed to have been formed at high temperature.     

The Effect of Al and Fe on the Intergranular Embrittlement of Co3Ti Alloys by Hydrogen Transport from the External Surface

1. IntroductionThe limited room-temperature tensile ductilityof illtermetallic alloys tested in air is now knownto arise from the hydrogen embrittlement process,which involves the surface reaction of active elements in intermetallics with water vapor in air alldgeneration of atomic hydrogen, leading to hydrogellembrittlement[1-7]. The Co3Ti alloys doped witll Alor Fe are much less susceptible to environmental elnbrittlement, indicating that the elements Al and Fein Co3Ti alloys have some su…     

Rapid Growth of TiNi intermetallic compound within undercooled Ti50Ni50 alloy under electrostatic levitation condition

The undercooling dependence of the solidification mechanism was systematically explored by the elec-trostatic levitation(ESL)facility.During the experiments,the maximum undercooling reached up to 406 K(0.26 TL)and the growth velocity of the primary TiNi phase was in-situ determined at various undercool-ings.At the initial increase of alloy undercooling,the value of growth velocity sluggishly rose followed by a power function.In this case,the primary TiNi phase preferentially developed as the equiaxed dendrite,then the remnant liquid participated as Ti2Ni and α-Ti phases on the grain boundary.Once the under-cooling exceeded the critical value of 350 K,the growth velocity of the primary phase displayed a sharply increase tendency.Meanwhile,the TEM results demonstrated that the precipitation of the intermetallic Ti2Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.     

Formation of submicrocrystalline structure in TiAl intermetallic compound

The TiAl intermetallic compound was used to illustrate an approach which enables the creation of a submicrocrystalline structure (d0.1 m) in massive semifinished products made of hard-to-deform materials by means of their deformation at elevated temperatures. Tensile mechanical properties of the TiAl intermetallic compound with a mean grain size of 0.4 m were tested. In this state, the lower temperature limit of superplasticity in TiAl was found to be 800°C. At this temperature and at an initial strain rate of 8.3×10^–4s^–1, the relative elongation to rupture attains 225%.