Yufeng Zheng

The tensile behavior of Ti36Ni49Hf15 high temperature shape memory alloy

Recently, ternary Ti-Ni-Hf alloys have attracted great interest in the field of high temperature shape memory materials research and development. Extensive studies have been made on its manufacture process, constitutional phases, phase transformation behavior, the structure, substructure and interface structure of martensite and the precipitation behavior during ageing. Yet up to date there is no report about the fundamental mechanical properties of Ti-Ni-Hf alloys, such as the stress-strain data, the variation laws of the yield strength and elongation with the temperature. In the present study, tensile tests at various temperatures are employed to investigate the mechanical behavior of Ti-Ni-Hf alloy with different matrix structures, from full martensite to full parent phase structure, with the corresponding deformation mechanism discussed.

Microstructural development inside the stress induced martensite variant in a Ti-Ni-Nb shape memory alloy

The microstructural development inside the stress induced martensite (SIM) variants in Ti-Ni-Nb alloy with various degrees of deformation have been revealed by electron microscopic observations. The orientation relationship between the SIM and the parent phase has been found: [1(1) over bar 0](M)//[11(1) over bar](B2), (001)(M) 5 degrees away from (101)(B2) The lattice invariant shear of the SIM variants at the slightly deformed stage is dominantly (11(1) over bar) Type I twin. Besides the ordinary slip, the adjustment and development of the internal secondary twinning from (11(1) over bar) Type I twin to [011] Type II/or (011) Type I twin, (001) compound twin and (111)Type I twin happen concurrently or in combination inside the SIM variants with the further deformation. The corresponding deformation mechanisms include stress induced reorientation of SIM substructural bands by the most favorably oriented twin system, stress induced migration of the SIM substructural boundary through internal twinning and stress induced injection of foreign SIM variant to the preexisting substructural bands

The structure and mobility of the intervariant boundaries in 18R martensite in a Cu-Zn-Al alloy

Abstract Detailed crystallographic analysis was carried out on the martensitic transformation and the various variant combinations in 18R martensite in a Cu–Zn–Al alloy. The self-accommodation of martensitic shear strain is quite perfect within a variant group, but not effective or even does not exist for variant combinations which belong to different groups. Twenty-three unique variant combinations between 24 martensite variants can be divided into four groups, i.e. reflection twin, 180° rotation twin, 120° rotation twin and 90° rotation twin. TEM and HREM observations show that the A/C boundary is straight, well-defined and perfectly coherent, the A/B boundary is irrational, coherent and gradually curved, and the A/D boundary is stepped. The A/C and A/B boundaries have obvious mobility, and the mobility is not effective for A/D boundary. The interplate group boundaries are curved, blurred and immobile. The morphology, structure and mobility of interplate boundary are all related to the degree of self-accommodation and the misorientation of twin boundary.

Substructure and boundary structure of deformed 18R martensite in a Cu–Zn–Al alloy

Abstract The substructure of martensite and the intervariant boundary structure in the deformed 18R martensite in a Cu–Zn–Al shape memory alloy have been investigated in detail by a high resolution electron microscope (HREM). It is found that the deformation-produced dislocations, which mainly appear in the (0018) plane, extend into partial dislocations with a spacing of 5–8 atomic layers. In addition to (0018)[010] slipping, dislocations in the ( 1 28) plane are also found. To accommodate strain, lattice rotation takes place near the boundary plane to bring close packed planes of the related variants into parallelism, reducing the resistance for the boundary to move. The intervariant boundaries in the same plate group or between different groups develop into stepped boundary structure due to deformation. These steps correspond to twinning dislocations whose movement results in the migration of the boundary perpendicular to itself.

Type II twins and their deformation characteristics in 18R martensite in a Cu–Zn–Al alloy

Abstract The A/B twin boundary (type II) in 18R martensite in a Cu–Zn–Al alloy was observed by high resolution electron microscopy. The two-dimensional lattice image suggests that the irrational interface is not a sharp ledge and step one, but gradually and randomly curved with a slight strain contrast. However, in response to applied stress, with invariant plane strain conditions, the boundary develops into a stepped structure.

High-resolution electron microscope observation of the non-basal planar defects in 18R martensite in a Cu-Zn-Al alloy

harbin inst technol, sch mat sci & engn, harbin 150001, peoples r china. chinese acad sci, inst met res, atom imaging solids lab, shenyang 110015, peoples r china.;zhang, jx (reprint author), harbin inst technol, sch mat sci & engn, harbin 150001, peoples r china

Effect of deposition and treatment conditions on growth of nanometer PtSi heterostructure

Under different substrate temperatures, deposition thickness, and annealing temperatures, the growth of nanometer-scale PtSi/p–Si(111) heterostructures prepared by sputtering was investigated by x-ray photoelectron spectrum (XPS), x-ray diffraction (XRD), and atomic force microscopy (AFM) techniques. The results of XPS show that the peaks of the Pt4f chemical binding energies of deposited Pt film specimens shift to higher energies after annealing. Pt, PtSi, and Pt2Si phases existing in the annealed film are verified by XRD. AFM observations prove that the surface morphologies are obviously different with different treatment conditions. The growth of the PtSi phase and the distribution of silicides are intensely affected by the deposition and technological parameters. It is also confirmed that Pt, PtSi, and Pt2Si phases coexist in the same layers. In the present study, the more uniform and flatter heterostructure film of PtSi/p–Si(111) is attained under the conditions with annealing temperature of 500u200a°C (...

High resolution electron microscope observation of two kinds of intervariant boundaries in 18R martensite in a Cu-Zn-Al alloy

harbin inst technol, sch mat sci & engn, harbin 150001, peoples r china. chinese acad sci, inst met res, atom imaging solids lab, shenyang 110015, peoples r china.;zhang, jx (reprint author), harbin inst technol, sch mat sci & engn, harbin 150001, peoples r china