Fabrication of in-situ synthesized ceramic reinforced Ni-based alloy composite coatings by reactive braze coating processing

In-situ synthesized ceramic such as TiC,Cr7C3 and Cr5B3 reinforced Ni-based alloy composite coating was fabricated on the surface of mild steel substrate by reactive braze coating processing with colloidal graphite,Cr,Ni,ferro-boron,Si and titanium powders as the raw materials at low temperature of 1000℃,and a new kind of coating materials was developed.By means of SEM,EDS,XRD and surface hardness tester,the microstructures,phases,hardness and wear-resistance of the coating were analyzed,respectively.The results revealed that the coating was mainly composed of the ceramic in-situ synthesized reinforcement phases of TiC,Cr7C3 and Cr5B3 and the binder phases in-situ synthesized of Ni31Si12 and(Ni,Fe)solid solution;The ceramic reinforcement phases of TiC,Cr7C3 and Cr5B3 were randomly distributed in the binder phases of Ni31Si12 and(Ni,Fe)solid solution;The coating had about 15vol%pores and can possibly be applied as a self-lubrication coating;The coating and the substrate were integrated together by metallurgical bonding;The coating had a hardness up to 91-94HR15N.

Microstructure and bonding strength of Ni-based alloy coating

A Ni-Cr-B-Si coating technique was developed and successfully applied on austenite grey iron substrate in a conventional resistance furnace under graphite powder protection. The microstructure, phase distribution, chemical composition profile and microhardness along the coating layer depth were investigated. Shear strength of the coating was also tested. Microanalysis shows that the coating is consist of γ-Ni solution and γ-Ni+Ni3B lamellar eutectic, as well as small amount of Cr5B3 particles. Diffusion induced metallurgical bonding occurs at the coating/substrate interfaces, and the higher the temperature, the more sufficient elements diffused, the broader interfusion region and the larger bonding strength, but it has an optimum value. And the bonding strength at the interface can be enable to reach 250-270 MPa, which is nearly the same as that of processed by flame spray. The microhardness along the coating layer depth shows a gradient distribution manner.

Fracture Behaviour of Laser Clad Fe-and Ni-base Alloy Coatings on a Cast Iron under SEMI Loading

Laser cladding technique has been applied to renovate some partially-damaged (or worn) components with Fe, Ni, Co-base alloys, hence to improve their hardness values and wear resistance successfully in previous reports. But for some punching or shearing cast iron dies damaged or worn in automobile manufacture, the renovated surfaces also bear some impact loading. Therefore, a small-energy and multi-impact (SEMI) test was designed to investigate the fracture behaviour of renovated cast iron dies achieved by laser cladding of Fe and Ni-base alloys under SEMI loading to meet above requirement. observations show that the fracture took place in the substrate near to the substrate/coating interface rather than at the interface. The tempering temperature has a great influence on the cycles to fracture of laser-clad samples under SEMl loading, i.e. the low tempering temperature of 300℃ gives a maximum cycle to fracture, while a higher tempering temperature of 400℃ has a minimum. Furthermore, the fracture mechanism has also been discussed in present study

EFFECT OF DUCTILE-BRITYLE TRANSITION TEMPERATURE OF Al-Si COATING ON FATIGUE PROPERTIES OF Ni-BASE SUPERALLOYS

The effect of Al content on the ductile-brittle transition temperature of Al-Si coating and the effect of fracture behaviour.of the Al-Si coating on the fatigue properties of Ni-base superallovs have been investigated to propose the theoretical basis of search for an optimum of mechanical properties of the high temperature coating on Ni-base alloys.

PROPERTIES OF YTTRALUMINIZING COATING ON Ni-BASE SUPERALLOYS

The yttraluminizing coating on the Ni-base superalloys has been developed by dipping the specimens in a specially made yttrium-containing slurry as an underlayer and over spraying a Cr-Al slurry as a protective layer,then heating to 1060℃ and holding for 1 h under argon atmosphere.Analysis by EPMA showed that the yttrium was concentrated in the intermediate zone of the coating as metallic compound Ni-5Y.After exposure to air up to 1000℃,the oxidation test revealed that the anti-oxidation resistance of the yttraluminizing coating with post-aluminizing is much superior to that with single aluminizing only.

Corrosion behavior of Ni-based coating containing spherical tungsten carbides in hydrochloric acid solution

A Ni-based alloy coating with 30 wt.%spherical fungsten carbide particles was prepared through plasma transferred arc welding on 42CrMo steel.The composition and microstructure of the coati ng were examined through X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry.The corrosion behaviors of the coating compared to the Ni coating without tungsten carbide particles and to the bare substrate in a0.5 mol/L HC1 solution were presented through polarization curves,electrochemical impedance spectroscopy(EIS)measurements and long-term immersion tests.The results demonstrated that the composite coating microstructure comprised Ni matrix,Ni-rich phase,tungsten carbide particles,W-rich phase and Cr-rich phase.The polarization curves and EIS measurements presented that a passivation film,which mainly included Ni,Cr,Fe and W oxides,was formed in the composite coating that protected the substrate from corrosion by HC1 solution.In the immersion tests,a micro-galvanic reaction at the new-formed phases and Ni matrix interface caused severe pit corrosion and Ni matrix consumption.The debonding of Ni-rich and W-rich phases could be observed with the immersion time extension.The tungsten carbide particles and Cr-rich phase were still attached on the surface for up to 30 days.

Influence of Hot Corrosion on High Temperature Creep Rupture for Single Crystal Superalloy DD3

nfluence of hot corrosion on the creep rupture behavior for both single crystal Ni-based superalloy DD3and specimens coated with Pt-Al was studied. In mixed salt, Pt-Al coating can improve creep properties of thealloy. The low melting point eutectic products lead to premature failure of alloy. This article proposes a newfracture model to explain the creep fracture behavior of DD3 at elevated temperature.

Fatigue behavior of uncoated and MCrAlY-coated DS nickelbased superalloys pre-exposed in hot corrosion condition

The effects of a MCrAlY coating on low-cycle fatigue(LCF) behavior of directionally solidified(DS)nickle-based superalloy DZ125 were investigated. Before the fatigue testings, the specimens were pre-exposed in high-temperature hot corrosion(HTHC) environment generating by a burner rig at 850 ℃. The results show that the coating in hot corrosion condition has beneficial effects on the fatigue resistance of superalloy. Under corrosion condition, the MCrAlY-coated specimens tested have higher fatigue lives than the uncoated specimens at the same stress level. The coating failure results from fatigue process and numerous fatigue cracks were nucleated at the specimen surface, only one main crack propagates inward and the secondary cracks away from the fracture surface are perpendicular to the loading orientation.