Papers by Author: Xiao Ping Lin

Abstract: In this study, we investigated the aging strengthening of Mg-Zn-Cu alloy based on component optimization design by FactSage software, optical microscope (OM), X-ray diffraction (XRD) and Vickers hardness tester. The results show that the precipitation rate of MgZn₂ phase in Mg-6Zn-1Cu is significantly higher than that of the other alloys. When Mg-6Zn-1Cu alloy is subjected to aging at 160°C for different time, the phase consists of α-Mg, MgCu₂ and MgZn₂. The content of main strengthening phase MgZn₂ is increasing with the prolonging of aging time. When Mg-6Zn-1Cu alloy aged at 160°C for 10h, the kinetics of precipitation is considerably accelerated. The results indicate that the hardening produced in the Cu-containing alloy is considerably higher than in the Mg-Zn alloy. Therefore, based on component optimization design to establish Mg-Zn-Cu alloy solidification database, and to predict the phase equilibrium and thermodynamic properties of the alloy, is an effective method for the development of new magnesium alloy.

Abstract: The microstructures of the Mg-6Zn-2Y alloy solidified under high pressures were investigated using scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The room-temperature compression behavior was analyzed through experiments, showing that the microstructures of the alloys are consisted of α-Mg and quasicrystal I-Mg3Zn6Y phases. With solidification pressure increasing, the microstructures were refined, and the morphologies of the inter-dendritic secondary phase were improved from continuous networks into long-island and granule. The compression strength, yielding strength and compressibility were increased significantly corresponding with solidification pressure, from 259.02 MPa, 230.39 MPa and 18.3% under ambient pressure to 361.43 MPa, 272.25 MPa and 33.1% under high pressure of 6 GPa. The cleavage planes are flat, and the cleavage steps are straight under ambient pressure. However, the cleavage planes are small and rough under 4-6 GPa; tearing dimples occur in the tearing area, indicating that the degree of cleavage fracture decreases under high pressure.

Abstract: The formation Gibbs energy of the intermetallic phases at the interface of cold rolling Cu/Al clad metal sheet in annealing process was calculated theoretically. The concept and the calculating method of effective formation Gibbs energy which can predict the formation sequence was proposed. By the means of that theory, the calculated formation sequence of the intermetallic phases at 200-300 was worked out for the cold rolling Cu/Al clad metal sheet in annealing process, i.e. Al₂Cu (Al side), AlCu (mid-layer) and Al₄Cu₉(Cu side). Besides, the boundary layer organizational microstructure of the composite material was analyzed by the means of SEM and XRD. As a result, the annealing temperature is the primary factor which affects the formation of the intermetallic phases of the cold rolling Cu/Al clad metal sheet, while the holding time is the second one. The observed formation sequence of the intermetallic phases of cold rolling Cu/Al clad metal sheet on annealing temperature 250-300 was: Al₂Cu (Al side), Al₄Cu₉(Cu side) and AlCu (mid-side).

Abstract: WC/Co; Composite coating; Plasma spraying; Friction and wear Abstract: WC- Co composite powders were synthesized by direct mechanical grinding in a rotary-vibration mill under 8h, and then analyzed by SEM and XRD. WC and WC/Co composite coatings were prepared by supersonic plasma spraying fine WC-Co composite powders. The wear and friction properties of both coatings were evaluated. The results showed that the wear resistance of the WC/Co composite coating was superior to that of the WC coating. The improvement in wear resistance of the WC/Co composite coating was attributed to its higher fracture toughness and adhesion strength as well as better thermal diffusivity. As for the WC/Co composite coating, the mechanism was mainly adhesion with micro-abrasion and fatigued-induced brittle fracture within splats, and the delamination along splat boundaries only occurred at high load. However, the failure of the WC coating was predominantly detachment of transferred film and brittle fracture within the splats and delamination along splat boundaries, which were enhanced with the increasing load.

Abstract: The solidification microstructure of Mg-6Zn-3Y alloy under super-high pressure was investigated by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the dendritic structure of Mg-6Zn-3Y alloy under super-high pressure (GPa level) can be evidently refined with the increase of solidification pressure. When the pressure increases to 2 GPa, Y element can’t solubilize in matrix of a-Mg, the primary Y solid solution is distributed in the shape of polygon block in the matrix. When the pressure is up to 4 GPa, the primary Y solid solution appears as symmetrical petaline shape. So Y solid solution exhibits the different morphology with the change of the pressure

Abstract: Macroscopic lattice deformation of martensitic transformation and shape memory effect (SME) were studied by atom force microscopy (AFM), X-ray diffraction and so on. The results showed that stress induced martensitic surface relief was “N”-shaped. The surface relief was parallel distribution when deformation was less than 6%. When relief became to intercross, its height and width were far less than parallel relief in same deformation. Superior heat-recovery was discovered in parallel surface relief. The recovery ratio was very low in intercrossed relief. The macroscopic lattice deformation descends in virtue of relief intercrossed, then recovery process was forbidden, so that recovery ratio was descent.

Abstract: The Al2O3 nano-films of different thicknesses (1~100nm) were successfully deposited on the monocrystalline Si surface by using ion beam sputtering deposition. The surface topography and the component of nano-films with different thickness were analyzed. The quality of the surface of nano-films was systematically studied. When the films’ thickness increase, the studies by atomic force microscope (AFM), X-ray photoelectron spectrum（XPS） show that the gathering grain continually grows up and transits from acerose cellula by two-dimensional growth to globularity by three-dimensional growth. The elements O, Al and Si were found on the surface of Al2O3 nano-films. With the thickness of the films increasing, the content of Al gradually increases and the intensity peak of Si wears off, the surface quality of the deposited films is ceaselessly improved

Abstract: Thermal barrier coating (TBC), which consisted of a NiCoCrAlY bond coat (BC) and a ZrO₂-8 wt.%Y₂O₃ topcoat (TC), was fabricated on the nickel-base superalloy by air plasma spray (APS). The BC and TBC was treated by vacuum heat treatment (VHT). The oxidation of coating with and without VHT has been performed at 1050°C. Oxidation behavior of coatings and thermally grown oxide(TGO) scale were studied by SEM with EDS. As shown in the results, after treating by VHT, a continuous Al₂O₃ layer formed more rapidly on the VHT coating than that formed on the APS coating, which can act as a diffusion barrier to suppress the formation of other detrimental oxides. The pre-oxidation treatments reduced the growth rate and extend the steady-state growth stage. The TGO in VHT TBC was still a single layer Al₂O₃ oxide after 120h. However, after same oxidation time, the TGO in APS TBC produced a dual-layer oxide consisting of an inner Al₂O₃ layer and outer spinel layer. Therefore the VHT improves the oxidation resistance of APS coating.

Abstract: In-situ spherical icosahedral quasicrystal phase (I-phase) was fabricated in Mg-Zn-Y-based alloys by metal mold casting route. The effects of Mn and/or Cu on spheroidized process, morphology and microhardness of primary I-phase were studied in this paper. The results showed that the solidified morphology of I-phase depended on the stability of spherical I-phase during the subsequent growth and critical radius Rr of the spherical I-phase. Only when actual radius smaller than critical radius Rr can spherical IQC be formed. The effects of the fourth component and degree of undercooling on Rr were studied for the first time. Amazing spherical minisize IQC had been produced by improving cooling rate using a water-cooled copper mold. Multicomponent spherical IQC is hopeful of being strengthening phase to novel metal composites.