An Al-Si coating was prepared on IC21 alloy by powder pack cementation. The cyclic oxidation tests were carried out at 1150 in air for up to 100 h. The results indicate that the oxidation resistance of IC21 alloy is significantly improved by the Al-Si coating due to the presence of Ni2Al3and β-NiAl enriched outer layer, and Si can effectively supress the outward diffusion of Mo. The oxide scales mainly consist of α-Al2O3, which is the favorite to the oxidation resistance. Phase transformation occurred from β-NiAl to γ-Ni3Al and γ-Ni in the coating during oxidation. The coating still remained a certain amount of β phase after oxidation for 100h, which indicate a good protection. The microstructure change evolution was characterized, and the oxidation behavior of the coating was discussed.

The oxidation kinetic curves of three Ni3Al-based single crystal alloys (IC21, IC21C and IC21CR) with different Cr and Re content were examined at 1100. The microstructures and element distributions of the oxide scales on these alloys were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectrometry (EDS). Results revealed that the oxidation resistance of these alloys was improved in the order of IC21 < IC21C < IC21CR. The oxide products of IC21 mainly consisted of NiO, α-Al2O3, NiAl2O4and a small amount of NiMoO4and MoO2. The volatilization of Mo oxides led to the oxide scale spallation from IC21C, thus deteriorated the oxidation properties. While for IC21C and IC21CR, the oxidation resistance was significantly improved. The Mo oxides in the oxide layer were greatly reduced and a continuous α-Al2O3layer was formed.

The influence of Al content on microstructure and creep behavior of Ni3Al-Base single crystal superalloy was investigated. Two Ni3Al-Base single crystal alloys with different Al contents were prepared in a vacuum induction furnace by screw selection crystal method.Optical microscope (OM), differential scanning calorimetry (DSC),scanning electron microscope (SEM),energy dispersive spectrometer (EDS),and X-ray diffraction (XRD) were used to observe the microstructure of the alloys.The experimental results showed thatthe volume fraction, mean size of the eutectic phase γ-γ′, γ′before and after heat treatment display differences with the Al content. It has been found that the stress-rupture lives increased with theAl content.The reasons may be as follows.Firstly, as content of Al increases, the reinforcing phaseγ′increases, resulting in the improvement of the precipitation strengthening.And secondly, the increasing of Al content leadsthe decreasing lattice mismatch of γ/γ′ phase, which enhances the coherent strain field around theγ′ phase and the hence increase the strengthening effect to the alloy.

The fretting wear performance of surface wear-resistant Cr3C2/Ni3Al composite deposited onto IC6SX alloy by manual argon tungsten-arc welding was investigated in this study. The results showed that the welded substrate exhibits a very good performance in comparison to the unwelded substrate at 500°C and 800°C, with 51.5% and 57.8% decrease of the fretting sectional area respectively. However, the fretting sectional area of the welded substrate is larger than that of the unwelded substrate at RT indicating poor fretting resistance as the reinforce phases of the welding layer is harder and more harmful to the sample surface. Examination of the fretting surfaces indicated that both the welded and unwelded samples undergo gross slip at RT and 500°C, and partial slip at 800°C. Coefficient of friction (COF) results were given by the SRV-4 tester which shows that as the temperature goes up, the COF of samples became lower and more stable. The results showed that the COF of welded substrate is lower than that of the unwelded substrate most of the time.

In this investigation, 3wt.% Ru was added to a low Cr and high W content superalloy with a nominal composition of Ni-10Co-1.5Cr-2.0Mo-1.0Nb-5.5Al-1.2Ti-0.1C-0.02B (wt.%) and both the Ru-free and the Ru-bearing alloys were directionally solidified. The multi-step heat treatment, thermal exposure and stress rupture test were performed. The results indicate that Ru is a weak positive segregation element (k’=Cinterdendrite / Cdendrite= 1.03). The solubility of Ru in γ phase is 30% higher than that of in γ' phase. Ru hardly enters into MC carbides, but can effectively retard the formation of M6C carbides. Ruthenium reduces the amount of eutectic (γ+γ'), decreases solid solution temperature of γ' phase, and promotes the rafting tendency of γ/γ' at elevated temperatures. Ru-bearing alloy possesses rather higher life at 1100°C/118MPa due to decrease of the film-like M6C carbides. The addition of Ru can inhibit the formation of M6C and eutectic γ', which hinder the initiation and propagation of cracks.