Peilei Zhang

Microstructure, Wear Resistance and Oxidation Behavior of Ni-Ti-Si Coatings Fabricated on Ti6Al4V by Laser Cladding

The Ni-Ti-Si composite coatings were successfully fabricated on Ti6Al4V by laser cladding. The microstructure were studied by SEM (scanning electron microscopy) and EDS (energy dispersive spectrometer). It has been found that Ti2Ni and Ti5Si3 phases exist in all coatings, and some samples have TiSi2 phases. Moreover, due to the existence of these phases, coatings presented relatively higher microhardness than that of the substrate (826 HV (Vickers hardness)) and the microhardness value of coating 3 is about twice larger than that of the substrate. During the dry sliding friction and wear test, due to the distribution of the relatively ductile phase of Ti2Ni and reinforcement phases of Ti5Si3 and TiSi2, the coatings performed good wear resistance. The oxidation process contains two stages: the rapid oxidation and slow oxidation by high temperature oxidation test at 800 °C for 50 h. Meanwhile, the value of the oxidation weight gain of the substrate is approximately three times larger than that of the coating 4. During the oxidation process, the oxidation film formed on the coating is mainly consisted of TiO2, Al2O3 and SiO2. Phases Ti2Ni, Ti5Si3, TiSi2 and TiSi were still found and it could be responsible for the improvement in oxidation resistance of the coatings by laser cladding.

Relationship between the γ and some parameters of Fe-based bulk metallic glasses

Abstract The relationship between γ (Tx/(Tg + Tl)) of Fe-based bulk metallic glasses (BMGs) and three parameters (i. e., electronegativity difference, atomic size parameter and heat of mixing) is studied in this paper. The conclusion can be drawn from the available experimental data in the literature that parameter γ has a close correlation to three parameters in Fe-based BMGs. It can be expressed as follows: γ = 0.40334 − 0.20242 × Δx2 − 0.1209 × δ2 + 3.7395 × 10−6 × ΔH2. The function can be obtained by a nonlinear regression analysis program and it can be used to find new Fe-based BMGs alloys.

Rapid prototyping of 4043 Al-alloy parts by cold metal transfer

ABSTRACT The macro-structure, microstructure and mechanical properties of 4043 aluminium-alloy parts manufactured by variable polarity cold metal transfer welding (CMT + Advance) have been investigated. The results showed that processing parameters have a strong effect on the geometry, microstructures, roughness and hardness of a deposited part. The problem of the hump and arc collapse was solved by the adjustment of specific welding parameters. Different morphologies were formed at different locations according to the observation of the microstructure. The elemental segregation was found between the layers of the component. The results showed that the dimensional accuracy of the single wall forming sample could be controlled much better by means of adjusting the parameters and optimising the path, thus excellent sample would be obtained.

Microstructures Evolution and Micromechanics Features of Ni-Cr-Si Coatings Deposited on Copper by Laser Cladding

Three Ni-Cr-Si coatings were synthesized on the surface of copper by laser cladding. The microstructures of the coatings were characterized by optical microscopy (OM), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS). According to the analysis results of phase compositions, Gibbs free energy change and microstructures, the phases of three coatings appeared were Cr3Si+γ-Ni+Cuss (Coating 1, Ni-26Cr-29Si), Cr6Ni16Si7+Ni2Si+Cuss (Coating 2, Ni-10Cr-30Si) and Cr3Ni5Si2+Cr2Ni3+Cuss (Coating 3, Ni-29Cr-16Si). The crystal growth in the solidification process was analyzed with a modified model, which is a combination of Kurz-Giovanola-Trivedi (KGT) and Lipton-Kurz-Trivedi (LKT) models. The dendrite tip undercooling in Coating 2 was higher than those of Coating 1 and Coating 3. Well-developed dendrites were found in Coating 2. A modification of Hunt’s model was adopted to describe the morphological differences in the three coatings. The results show that Coating 1 was in the equiaxed dendrite region, while Coatings 2 and 3 were in the columnar dendrite region. The average friction coefficients of the three coatings were 0.45, 0.5 and 0.4, respectively. Obvious plastic deformation could be found in the subsurface zone of Coatings 2 and 3.