Huibin XU
,
Shuqiang HU
,
Chengbao JIANG
,
Shengkai GONG
材料科学技术（英文）
The high temperature shape memory alloy Ti51Ni13Pd36 was subjected to a cold working and annealing treatment to improve its mechanical properties and the shape memory effect. It was found that recovery of the cold worked alloys started at near 673 K and the recrystallization temperature was at about 748 K. The grain size decreased with the increase of annealing temperature below 923 K and then increased when above 923 K. The smallest average grain size of about 3.5 mu m, which is approximately 10 times smaller than the hot rolled one, permitted the best combination of the mechanical properties in the alloy annealed at 923 K for 1 h. The cold rolling raised the peak temperature of reverse transformation. This temperature dropped very sharply when the specimen was annealed at temperatures higher than 673 K.
关键词:
Chungen ZHOU
,
Jingsheng YU
,
Shengkai GONG
,
Huibin XU
材料科学技术（英文）
The oxidation of specimens with thermal barrier coating (TBC) consisted of nickel-base superalloy, low-pressure plasma sprayed Ni-28Cr-6Al-0.4Y (wt pct) bond coating and electron beam physical vapor deposited 7.5 wt pct yttria stabilized zirconia (YSZ) top coating was studied at 1050℃ respectively in flows of O2, and mixture of O2 and 5%H2O under atmospheric pressure. The thermal barrier coating has relatively low oxidation rate at 1050℃ in pure O2. Oxidation rate of thermal barrier coating in the atmosphere of O2 and 5%H2O is increased The oxidation kinetics obeys almost linear law after long exposure time in the presence of 5% water vapor. Oxide formed along the interface between bond coat and top coat after oxidation at 1050℃ in pure O2 consisted of Al2O3, whereas interfacial scales formed after oxidation at 1050℃ in a mixture of O2 and 5%H2O were mainly composed of Ni(Al,Cr)2O4,NiO and Al2O3. It is suggested that the effect of water vapor on the oxidation of the NiCrAlY coating may be attributed to the increase in Ni and Cr ions transport in the oxides.
关键词:
Oxidation
,
null
,
null
Fei CAI
,
Chungen ZHOU
,
Huibin XU
,
Shengkai GONG
材料科学技术（英文）
An oxidation resistant Al-Cu-Fe quasicrystalline coating was fabricated on substrate of Ti alloy by low pressure plasma spraying (LPPS) method. As-sprayed Al-Cu-Fe coating has a rapidly solidified lamellar microstructure consisting of quasicrystalline phase and crystalline phase. The formation of quasicrystalline coating is related to the annealing. The results from the oxidation experiments showed that Al-Cu-Fe quasicrystalline coating improved the oxidation resistance of Ti-base alloys. During the oxidation period there is no evident spallation of the coating from the substrate. Oxide formed on the surface of Al-Cu-Fe quasicrystalline coating after oxidation consisted of Al¬2O¬3. Oxidation occurs leading to a change of concentration and phase transformation in the coating surface. Selective oxidation of Al transforms the quasicrystalline phase into the phase.
关键词:
Low pressure plasma spray
,
null
,
null
,
null
,
null
Hongbo GUO
,
Shengkai GONG
,
Huibin XU
材料科学技术（英文）
The performances of gradient thermal barrier coatings (GTBCs) produced by EB-PVD were evaluated by isothermal oxidation and cyclic hot corrosion (HTHC) tests. Compared with conventional two-layered TBCs, the GTBCs exhibite better resistance to not only oxidation but also hot-corrosion. A dense Al2O3 layer in the GTBCs effectively prohibites inward diffusion of O and S and outward diffusion of Al and Cr during the tests. On the other hand, an "inlaid" interface, resulting from oxidation of the Al along the columnar grains of the bond coat, enhances the adherence of Al2O3 layer. Failure of the GTBC finally occurred by cracking at the interface between the bond coat and Al2O3 layer, due to the combined effect of sulfidation of the bond coat and thermal cycling.
关键词:
Gradient thermal barrier coating (GTBC)
,
null
Na WANG
,
Chungen ZHOU
,
Shengkai GONG
材料科学技术（英文）
The nanostructured zirconia coatings were deposited by atmospherically plasma spraying. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction were used to investigate the microstructure of the zirconia coatings. Thermal diffusivity values at normal temperatures have been evaluated by laser flash technique. Effect of annealing on the microstructure evolution of the zirconia coating has been performed. The grains and thermal diffusivity are increased with increasing annealing time and temperature. The grain growth is according to the GRIGC (the grain rotation induced grain coalescence) mechanism. The increase in thermal diffusivity is attributed to the grain growth and the decrease in porosity of nanostructured zirconia coatings.
关键词:
Grain size
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null
,
null
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null
