Study On Microstructure And Properties Of Ni-Al Intermetallic Compound Coating By Laser Cladding

Compared to other surface coating technology, laser cladding can prepare compact and good adhesion coating. Ni-Al intermetallic compounds, which have high melting point, low density and good high temperature performance, are expected to a new generation of high temperature structural materials.Coating prepared by laser cladding can effectively improve the performance of substrate material.In this paper, Ni-Al intermetallic compound coating were prepared on Q235 steel substrate according to the NiAl and Ni3Al composition range.The influence of laser cladding parameters on the coating quality were systematically studied and the optimal process parameters for preparing Ni-Al coating were obtained. Scanning electron microscope, X-ray diffraction, EDS energy spectrum were used to detect the micro structure and phase of the coatings. The hardness, adhesion, friction and wear resistance, high temperature oxidation resistance and thermal shock resistance of the coating were tested. The results show that:Laser cladding parameters can influence and restrict each other and have great influence on the quality of the coating, The best processing parameters were got by exploring the influence of various parameters on the quality of coating forming:powder paving thickness lmm, laser scanning speed of 2mm/s, laser current 300A, laser pulse width 2.5ms, frequency 20Hz.The micro structure of the Ni-Al coatings are uniform and fine, without obvious crack but with a small amount of pores. A good metallurgical bonding is formed between the substrate and the coating. The thickness of the coating is about 60～70μm. From the bottom to the surface of the coating, the micro structure is transformed from a strip of dendrite into an equal axial grain. When the cladding powder Ni, Al atomic ratio is 1:1, the coating is mainly composed of P-NiAl and a small amount of γ’-Ni3Al, and the γ’-Ni3Al is surrounded by a network of β-NiAl; When the cladding powder Ni, Al atomic ratio is 3:1, the coating is mainly composed of γ’-Ni3Al and γ-Ni, the γ’-Ni3Al is about 2 times as much as that of γ-Ni.Ni-Al coating can significantly improve the hardness of substrate. NiAl coating has the highest hardness and the average hardness is up to 659HV0.2, the average hardness of Ni3Al coating is 556HV0.2, the hardness of Q235 is only 200HV0.2. Adhesion between the coating and the substrate is fine, the adhesion of Ni3Al coating is better than NiAl coating.Ni-Al coating have better anti-friction ability and the friction coefficient is lower than substrate. The main wear mechanisms are severe plastic deformation and fatigue spalling for substrate, adhesive wear and a small amount of abrasive wear for NiAl coating, abrasive wear for Ni3Al coating. Q235 substrate has the biggest wear rate, The wear rate of Ni-Al coating is close to that of Cr15Mo3 steel, and the wear resistance of NiAl coating is stronger than that of Ni3Al coating.The dense Al2O3 protective film is formed on the surface of Ni-Al coating at high temperature, which has good high temperature oxidation resistance. In 900℃ temperature oxidation experiments, using the inverse of oxidation weight to characterize high temperature oxidation resistance, The high temperature oxidation resistance of NiAl coatings is about 7 times of that of the substrate, the Ni3Al coating is about 4 times of that of the substrate, the high temperature oxidation resistance of NiAl coating is stronger than Ni3Al coating.In 850℃ thermal cycling test, the thermal shock resistance of Ni-Al coating is close to conventional ZrO2-7% Y2O3 thermal barrier coating and nano ZrO2-7% Y2O3 thermal barrier coating. Ni3Al coating began to crack after 45 thermal cycles, NiAl coating began to appear after 70 thermal cycles. The thermal shock resistance of NiAl coating is better than Ni3Al coating.