Authors: Ying Chun Wang, Jian Guo Li, Yaohe Zhou
Abstract: Hydroxyapatite(HAP) has excellent osteoconductive properties. By controlling the Ca/P
ratio better biphasic calcium phosphate ceramics can be produced than pure HAP ceramics. β-
calcium pyrophosphate(β-Ca2P2O7) is a new biodegradable ceramic material and its biological
response is quite similar to HAP. Obtaining HAP and other bioactive calcium phosphate ceramic
coatings has been a popular research field in the past. In our research a new bioceramic composite
coating was obtained by laser cladding with pre-depositing mixed powders of CaHPO4·2H2O and
CaCO3 directly on the metal substrate. Its main constituents are HAP and β-Ca2P2O7. The
microstructure of the coating consists of minute granular HAP that is distributed among the
overlapped club-shaped or needle-like β-Ca2P2O7. The hardness distribution in the cladding layer is
even and its value is much higher than that in the substrate. There is a bonded structure of the
epitaxial planar growth between the substrate and cladding layer, and both a typical cellular
microstructure in the middle and an equiaxed microstructure at the top of the cladding layer.
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Authors: Zhen Bing Cai, Min Hao Zhu, Xiu Zhou Lin, Ji Liang Mo, Zhong Rong Zhou
Abstract: Nickel base Ni60 and cobalt base Co-Cr-W coatings were prepared on substrate of
refractory alloy steel 4Cr14NiW2Mo by laser-cladding technology. A 2 kW transverse-flowing CO2
laser device was used for cladding alloy powder. Another Co-Cr-W coating was formed by bead
welding. Under room temperature, 250 oC.and 420 oC, reciprocate sliding wear tests with a
ball-on-flat contact for three coatings have been carried out. For the laser cladding coating, a good
metallurgical bonding with the substrate was obtained. Different tribological behaviors of three
coatings were observed. For the two Co-Cr-W coatings, the friction coefficients decreased with the
increase of test temperature, and larger spot-like stripping pit and wider ploughing trenches in the
wear scars were presented. The wear mechanism was the combination of abrasive wear,
delamination and oxidation wear. For the Ni60 laser cladding layer, the friction coefficient hardly
changed with the elevated temperature, and the wear mechanism mainly performed as abrasive wear
due to its high oxidation resistance. The wear tests showed that the Ni60 clad coating had provided
excellent wear resistance than Co-Cr-W layers under high temperature reciprocating sliding wear
condition.
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Authors: Lei Zhao, Rong Lu Sun, Yi Wen Lei
Abstract: NiCrBSi+Ti+C and NiCrBSi+TiC composite coatings were fabricated on H13 steel substrate by laser claddings to improve its wear resistance. The macroscopic qualities of the coatings were analyzed and the process parameters and the clad materials were optimized. The microstructure of the coatings was characterized by SEM. The microhardness of the coatings was examined using HXD-1000 microhardness tester. The wear properties were examined using M-200 wear test machine. The results show that the clad materials and the process parameters are the important factors to influence the quality of laser cladding. Ni+Ti+C organization is smaller, particle strengthening and grain refinement is more significant. The hardness of the clad coating of NiCrBSi+Ti+C coatings reaches HV900, which is improved by almost three times compared with the substrate H13 steel.
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Authors: Xin Tong, Ming Jiang Dai, Min Liu
Abstract: Die-casting plunger often fails due to serious wear on its cylindrical surface. The scrap of plunger used in large die-casting machine results in waste of materials and energy sources, and it is also against environmental protection. Therefore, the laser remanufacturing of die-casting plunger was studied in this paper. Both of the size and the performance of plungers were repaired by laser cladding surface modification using an iron-based self-fluxing alloy. The interface between original failed plunger and laser cladding layer showed a good metallurgical bond. The average thickness of laser cladding layer was 0.845 mm, and the average micro-hardness reached to 750 HV upwards. Microstructure in laser cladding layer was composed by the dendrite primary phase and the ledeburite organization. Iron (Fe), Chromium (Cr) and Molybdenum (Mo) elements were the main chemical compositions measured in laser cladding layer. The service life of laser remanufacturing plunger was nearly the same as the life of new plunger. However, its remanufacturing cost was only 50% of the new plunger’s. The laser remanufacturing technique is worth for extending and applying due to high cost performance.
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Authors: Jian Hong Wang, Pei Kang Bai, Zhen Lin Zhang, Yu Xin Li
Abstract: Laser surface cladding of Ti6Al4V alloy by Ti+Al+C powders (Titanium and carbon powders with an atomic ratio of 1:1 were mixed with 20-60wt.% aluminum powders) was investigated using CO2 laser. TiC particles were in situ formed mainly during the solidification and sizes of TiC particles were varied according to different contents of aluminum powders in the Ti+Al+C system. The results show that the coating had good metallurgical bonding with substrate when Al content was 20% or 40%. The microhardness of coating is 738HV0.5 which was 2 times as that of the Ti6Al4V alloy approximately. The wear resistance of TiC/Al ceramic layer was approximately 3 times greater than that of the Ti6Al4V substrate. 1
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