Shoujun Wu

Preparation of titanium carbide-titanium boride coatings on Ti6Al4V by PIRAC

Abstract In the present work, titanium carbide–titanium boride coatings are prepared on Ti6Al4V by powder immersion reaction assisted coating (PIRAC). Microstructure and phase composition of the gained surface layers are characterised by X-ray diffraction and scanning electron microscopy equipped with energy dispersive spectrometer. Results show that homogeneous titanium carbide–titanium boride coatings can be formed on the substrate. Phases of the prepared coatings are co-existed TiC, TiB and TiB2 and their content varies with PIRAC treatments. Hardness of the titanium carbide–titanium borides coating prepared at 900°C is about 24·5 GPa, while that of prepared at 1000°C is about 22·5 GPa and shows a larger scatter.

Titanium Nitride Coatings on Ti Alloys by PIRAC for Orthopedic Implants

In the present work, Ti and Ti-6Al-4V were PIRAC nitrided at the relatively low temperatures of 700-850°C. To obtain thicker TiN layers, 3 stage PIRAC based coating was applied: (1) PIRAC nitriding followed by (2) PIRAC titanizing followed by (3) additional PIRAC nitriding. The microstructure and phase composition of the obtained surface layers were characterized employing X-ray diffraction and scanning electron microscopy with chemical analysis (SEM/EDS). Bending test was employed to evaluate the coatings adhesion to the substrate. Lower PIRAC nitriding temperatures yielded smoother TiN coatings with a more gradual microhardness decrease from the surface to the bulk. All PIRAC TiN based coatings have excellent adhesion to substrate – no delamination of the coating in bending tests was observed. The best combination of microhardness and adhesion was obtained using 3 stage PIRAC process.

Flexural Strength Distribution of 3D SiC/SiC Composite

Flexural strength of a four-step, three-dimensional (3D) braiding SiC/SiC composite was tested at room temperature. The strength distribution was studied based on Weibull distribution and Normal distribution as well as examined by the Kolmogorov test. The results indicated that the flexural failure behavior of the composite was rather brittle with a small displacement. And the statistical strength distribution of the 3D SiC/SiC composite was in agreement with two-parameter Weibull distribution of the Weibull modulus,m=8.1545 and normal distribution. And the predicated mean flexural strength of the 3D SiC/SiC composite by the two-parameter Weibull distribution was consistent with the tested value.

Modified curvature method for residual thermal stress estimation in coatings

Abstract In the present work, a modified curvature method for residual thermal stress estimation in coating/substrate was presented. The method based on the assumption of the classical beam theory was individually applicable to the coating and the substrate; besides, they were well bonded, continuous, homogeneous and isotropic. Analyses indicated that the residual thermal stress in the coating and substrate increased with increase in the difference in Young’s modulus, the average coefficient of thermal expansion and thickness of the coating and the substrate. Comparative analyses were performed according to some published experimental results. Results showed that the present estimation method is simple and valid.

Effect of Field Irrigation on Tensile Behaviors of Disposable Drip Tapes Made from Virgin PE

In the present work, effect of field irrigation on tensile behaviors of disposable drip tape made from virgin PE is studied. Results show that after 5 months (from Novomber, 2012 to next April, 2013) field irrigation tests, there are no intrinsically changes in tensile stress-strain behaviors for the disposable drip tape made from virgin PE along the longitudinal direction. Tensile stress-strain behaviors for the disposable drip tape made from virgin PE along transverse direction is different. After field irrigation tests, the tapes are prone to sudden rupture at the seams accompanied with a relative smaller elongation and acute stress drops while those as-received show large elongation with gradual stress decrease under transverse tensile. However, rebound of the stretched tapes after field irrigation tests is distinctly smaller than those of as-received samples.

Mechanical Self-adaptability of a SiC/PyC/SiC Composite During Oxidation in Air:

An oxidation test for three-dimensional (3D) SiC/PyC/SiC composite with CVD SiC coating was performed by thermogravimetric analysis (TGA) in simulated air at temperatures ranging from 600 to 1100°C. After oxidation, the mechanical properties were evaluated by a three-point flexural test. Effects of oxidation on mechanical properties of the composite were investigated by comparing the strength and failure behaviors as well as the morphologies examination. The results showed that the failure of the as-received composite was rather brittle while that of the oxidized composite showed a non-brittle pattern. Combining the oxidation analysis with a mechanical test, the result indicated that a certain extended oxidation of the PyC interphase led to an increased toughness without strength degradation due to improved interphase bonding in the SiC/PyC/SiC, namely, the composite showed mechanical self-adaptability with improved strength and toughness. The amount and length of fiber pull-out in the as-received composites were much smaller in comparison with those of oxidized composites.An oxidation test for three-dimensional (3D) SiC/PyC/SiC composite with CVD SiC coating was performed by thermogravimetric analysis (TGA) in simulated air at temperatures ranging from 600 to 1100°C. After oxidation, the mechanical properties were evaluated by a three-point flexural test. Effects of oxidation on mechanical properties of the composite were investigated by comparing the strength and failure behaviors as well as the morphologies examination. The results showed that the failure of the as-received composite was rather brittle while that of the oxidized composite showed a non-brittle pattern. Combining the oxidation analysis with a mechanical test, the result indicated that a certain extended oxidation of the PyC interphase led to an increased toughness without strength degradation due to improved interphase bonding in the SiC/PyC/SiC, namely, the composite showed mechanical self-adaptability with improved strength and toughness. The amount and length of fiber pull-out in the as-received composi...

Effect of Yttria Nanopowder on Multi-Layer Coatings of Yttria And CVD SiC/Graphite

Nano-yttria powder can be synthesized by yttrium citrate-urea precursor, combusted at 600°C in air. The CVD SiC coated on graphite (CVD SiC/Graphite) infiltrated by the yttrium citrate-urea precursor, combusted at of 600°C, and then sintered at 1450°C, the thin yttria film can be achieved. The SEM morphology and EDS result of the thin yttria film show a mass of needle-shaped pining into the CVD SiC layer, which improves the combination of CVD SiC layer and wash yttria coating. Therefore, it is an effective transition layer between CVD SiC coating and wash yttria layer.

Residual Stress And Fracture Toughness Of Pirac Titanium Nitride Coatings

In this work, residual stress and fracture toughness of titanium nitride coatings prepared by powder immersion reaction assisted coating (PIRAC) at 700∘C with different processing times are studied. Results show that the residual stress in the coatings is compressive stress and increases with processing times increasing. Indentation fracture toughness of the PIRAC coatings increased with processing times (coatings’ thickness) increasing. The fracture toughness of the coatings prepared at 700∘C with a processing time of 144h and 192h is 6.88±0.20MPa⋅m1∕2 and 9.15±0.15MPa⋅ m1∕2, respectively. Bending induced crack propagation in the coating shows multi-deflection mode which is beneficial to energy absorption and thus improved fracture toughness.

Solid reaction between Al and B4C

Abstract In the present work, solid reaction products formed by a mixture of aluminium and boron carbide (B4C) powder heat treated under low pressure were studied. No significant reaction between B4C and Al could be detected for reaction temperatures of 600°C or less. However, at 640°C, and over a short treatment time (1 h), a solid reaction took place between boron carbide and aluminium with the formation of A13BC and AlB2. Meanwhile, over a longer treatment time (36 h), the detectable product phase between boron carbide and aluminium was AlB12.

Hardness And Elastic Modulus Of Titanium Nitride Coatings Prepared By Pirac Method

In the present work, hardness and elastic modulus of a titanium nitride coatings prepared on Ti6Al4V by powder immersion reaction-assisted coating (PIRAC) are tested and comparatively studied with a physical vapor deposition (PVD) TiN coating. Surface hardness of the PIRAC coatings is about 11GPa, much lower than that of PVD coating of 22GPa. The hardness distribution profile from surface to substrate of the PVD coatings is steeply decreased from ∼22GPa to ∼4.5GPa of the Ti6Al4V substrate. The PIRAC coatings show a gradually decreasing hardness distribution profile. Elastic modulus of the PVD coating is about 426GPa. The PIRAC coatings show adjustable elastic modulus. Elastic modulus of the PIRAC coatings prepared at 750∘C for 24h and that at 800∘C for 8h is about 234 and 293GPa, respectively.