Microstructure and Wear Resistance of Si-TC4 Composite Coatings by High-Speed Wire-Powder Laser Cladding

The hardness and wear resistance of the surface of TC4 titanium alloy, which is widely used in aerospace and other fields, need to be improved urgently. Considering the economy, environmental friendliness, and high efficiency, Si-reinforced Ti-based composite coatings were deposited on the TC4 surface by the high-speed wire-powder laser cladding method, which combines the paraxial feeding of TC4 wires with the coaxial feeding of Si powders. The microstructures and wear resistance of the coatings were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness tester, and friction and wear tester. The results indicate that the primary composition of the coating consisted of α-Ti and Ti5Si3. The microstructure of the coating underwent a notable transformation process from dendritic to petal, bar, and block shapes as the powder feeding speed increased. The hardness of the composite coatings increased with the increasing Si powder feeding rate, and the average hardness of the composite coating was 909HV0.2 when the feeding rate reached 13.53 g/min. The enhancement of the microhardness of the coatings can be attributed primarily to the reinforcing effect of the second phase generated by Ti5Si3 in various forms within the coatings. As the powder feeding speed increased, the wear resistance initially improved before deteriorating. The optimal wear resistance of the coating was achieved at a powder feeding rate of 6.88 g/min (wear loss of 2.55 mg and friction coefficient of 0.12). The main wear mechanism for coatings was abrasive wear.

[Revascularization of isolated bone in dogs]

To elucidate whether the revascularization of isolated bone could be built and what is the influence on osteogenesis. We studied eighteen adult mongrel dogs and divided them into three groups in random. Osteotomy was performed on the two condyles of the tibia and the periosteum was removed. Two pieces of silica gel sheet were inserted into the gaps of osteotomy to block blood supply, then immobolization was made. The vascular bundle of anterior tibia artery and vein was separated and ligated. Subsequently, it was directly implanted into the isolated bar of tibia (Group A, n = 7). It implanted after holes were made (Group B, n = 7). Controls (Group C, n = 4) were observed without transplantation. The animals were investigated by angiography, casting mode of vascular net, mass and histologic and electromircroscopeic examination at different intervals. Osteonecrosis was occurred in the tested bone because of ischemia. The proliferation of vascular net was occurred and prosperous osteogenesis was found in the medullary cavity after transplanting a vascular bundle. Revascularization of necrotic bone was able to be established by transplanting a vascular bundle. Both membranous and lndochondral ossification play an important role in osteogenesis.