Lin Dongliang

LPSO STRUCTURE AND AGING PHASES IN Mg-Gd-Zn-Zr ALLOY

为了研究Mg-Gd-Zn-Zr合金中的长周期堆垛有序（LPSO）结构的形成及其演化,对铸态、固溶态和时效态Mg（96.32）Gd（2.50）Zn（1.00）Zr（0.18）合金的显微组织进行了观察.OM,SEM和TEM观察表明,合金铸态组织由α-Mg固溶体、晶内层片状14H-LPSO结构和晶界处树枝状α-Mg＋β-（Mg,Zn）3Gd共晶相组成;500℃/35 h固溶处理后,晶界处发生β→X的固态相变,层片状X相也具有14H-LPSO结构;再经200℃/128 h峰时效处理后,晶内析出椭球状β′相和片状β1相与14H-LPSO结构共存.室温拉伸实验和Vickers硬度测试表明,500℃/35 h＋200℃/128 h处理改善了合金的力学性能,抗拉强度为290.7 MPa,屈服强度为162.5 MPa,Vickers硬度为108.0 HV,延伸率为10.4%.力学性能的改善与晶界、晶内的14H-LPSO结构及时效相等复合强韧化作用有关.

Dislocation behaviour during cyclic deformation of niobium single crystals

Abstract Dislocation structures formed during cyclic deformation of niobium single crystals have been studied. Single crystals of both [321] and [110] orientations have been cyclically deformed in tension-compression under strain control. Moreover, the mechanical property data are supplemented by the direct observation of dislocation arrangements by transmission electron microscopy. In the case of [321] orientation single crystals the hardening curve can be divided into three stages, i.e. first, rapid-hardening and saturation stages associated with various dislocation structures. In the first stage the dominan features of the dislocation configurations are high density networks and debris loops. In the rapid-hardening stage the main feature is the formation of dislocation bundles. In the saturation stage the characteristic features are the dislocation bundles and the screw dislocations between bundles. The imposed strain is accomodated mainly by the motion of screw dislocation travelling to and fro between the bundles. For the [110] orientation single crystals the hardening curves are similar to those of the [321] orientation except that dislocation bundles of more than one direction appear during the first few cycles. Three-dimensional cell, two-dimensional cell and bundle structures are summarized as the saturated dislocation structures of b.c.c. metals.

COMPUTER SIMULATION OF DISLOCATION CORES IN B2 NIAL INTERMETALLICS

AbstractUsing embedded atom method and molecular static relaxation method, the core structure of 〈100〉, 〈110〉 edge dislocations, 〈100〉 screw dislocation, the interaction between point defects and 〈100〉 edge dislocation in NiAl intermetallics were investigated. The results show that 〈100〉 edge dislocation expands along [110] and

The effects of thermal annealing on defect configurations in SI-GaAs

[\bar 111]

ROLE OF SOLUTION TREATMENT IN IMPROVING THE CREEP STRENGTH OF A DIRECTIONALLY SOLIDIFIED NICKEL-BASE SUPERALLOY

orientation on the (001) slip plane. The core structure of 〈100〉 edge dislocation on (001) plane is like a ”butterfly”, while it is very compact when it lies on {110} slip plane. So NiAl will have a 〈100〉 {110} slip system in stead of 〈100〉 {100} slip system, as experiments showed. 〈110〉 edge dislocation has a more expanded core structure and the atoms of dislocation core distort more heavily. None dislocation dissociation was found in the studied dislocations. The outlines of dislocation core structures change very little after a row of point defects are introduced in them, which can be explained by point defects’ little effects on the stress field around dislocation core. The results also show that it is hard to change dislocation core structure by decreasing alloy order using the method of introducing limited point defects into the alloy.

Research Progress of Advanced Magnesium Rare-Earth Alloys

The superplastic behavior of a NiAl and Ni{sub 3}Al duplex alloy was investigated. It was found that the alloy exhibits superplastic behavior over a narrow temperature range, from 975 C to 1,025 C at the strain rate of 1.52 {times} 10{sup {minus}4}s{sup {minus}1}. A maximum tensile elongation of 149% was obtained at 1,000 C with the strain rate sensitivity up to 0.375. The superplastic deformation of the duplex alloy can be approximately described by an empirical equation of the form: {dot {var_epsilon}} = Ao{sup 2.67} exp({minus}303,000/RT). Optical microstructure and TEM observation show that the superplastic behavior mechanism of the investigated alloy is a process of continuous recovery and recrystallization during deformation.

SUPERPLASTICITY BEHAVIOURS OF Ni_3Al ALLOY WITH 10-30μm GRAIN SIZES

Abstract Crystal defects in semi-insulating GaAs have been characterized with TEM. The effects of thermal annealing on the defect configurations were investigated and the improvement of structural perfection and uniformity across GaAs wafers by annealing was found to be, mainly, due to the activation of individual dislocations and dislocations in loose groups.