Papers by Keyword: NiAl

Abstract: The isothermal oxidation behavior of NiAl-30.9Cr-3Mo-0.1Dy alloy has been investigated in the paper. The results reveal that Dy-addition significantly improves the oxidation resistance, which is attributed to the formation of continuously compact Al2O3 layer and rich-Cr transition layer on the surface of the tested alloy.

Abstract: The paper presents the preliminary research results that were aimed at working out a technology of the surface roughness reduction by means of plastic working methods. The intermetallic phase NiAl and Ni3Al coatings that were plasma sprayed on a flat bar made of non-alloy steel (C45) were chosen for the research. The coatings underwent plastic working with the use of press. Three specific loads were used: 500, 800, 1100 MPa. The treated coatings exhibited 70% lower surface roughness as compared to thermally sprayed layers. However, high values of relative strain of coatings ( = 0.21 – 0.62) were obtained. Plastic working resulted in the decrease of corrosive potential values and increase of corrosive current density.

Abstract: Starting from some fundamentals of solid-state diffusion, we remind the reader to the major techniques for lattice diffusion measurements. Self-diffusion is the most basic diffusion phenomenon in any solid. The paper covers main features of self-diffusion in pure fcc and bcc metals and some important facts about diffusion of substitutional solutes in metals. Binary intermetallics are compounds of two metals or of a metal and a semimetal. Their structures are different from those of the constituents. Some intermetallics are interesting functional materials others have attracted attention as high-temperature structural materials. The paper reviews some results mainly from our laboratory on diffusion in binary intermetallics from the systems Cu-Zn, Ni-Al, Fe-Al, Ni-Ge, Ni-Ga, Fe-Si, Ti-Al, Ni-Mn, Mo-Si and Co-Nb, which have been published in detail elsewhere. Some results for the ternary system Ni-Fe-Al are also mentioned.

Abstract: Lotus-type porous NiAl and Ni3Al intermetallic compounds, possessing cylindrical pores aligned in the direction parallel to the solidification direction, were fabricated by using a unidirectional solidification technique in a pressurized hydrogen atmosphere of 2.5MPa. The porosity of lotus NiAl is 24.2 %, and the porosity of lotus Ni3Al is 3.2%; the porosity of the porous NiAl is larger than that of Ni3Al. This is because the solubility gap of hydrogen between liquid and solid phases of NiAl is larger than that of Ni3Al.

Abstract: The influence of YSZ addition on isothermal oxidation behavior of EB-PVD NiAl bond coatings on Ni based superalloy was investigated. The oxidation rate of the YSZ doped bond coat is almost the same as the bond coat without the doping of YSZ. Four different areas exist on the surface of the coating after 100 h oxidation, including the spalled area, the high Al-contained area, the high Cr&Ni-contained area and the high Ti-contained area.

Abstract: The paper presents the results of the examination of nanocrystalline NiAl-TiC composites with 25 wt.% and 40 wt.% of TiC. The starting materials were coarse-grained powders which were subjected to mechanical refining to obtain a nano-crystalline grain size. These powders were then sintered using the pulse plasma method. After sintering the NiAl-TiC composites have a density of 99.9% of the theoretical value. The grain size, determined by X-ray diffraction using the Hall-Williamson method; density; hardness and fracture toughness of the composites were investigated. The results obtained showed that the pulse plasma sintered NiAl-TiC have a density very close to the theoretical value and that the nano-crystalline microstructure was maintained. The NiAl-TiC composites containing 25wt.% of TiC have a hardness of 750 HV1 and a stress intensity factor KIC of 7 MPa⋅m1/2, whereas those containing 40 wt.% of TiC have a hardness of 1070 HV1 and KIC of 11.8 MPa⋅m1/2.

Abstract: Directional or single crystal technique was applied to enhance the ductility, and two phases of γ (Ni) phase or β (NiAl) phase in γ‘(Ni3Al) matrix were also considered to increase the strength and ductility. In this study, directionally solidified rods were prepared at the solidification rate of 50µm/s in 23-27 at.% Al-Ni alloys, and tensile strengths of these rods were analyzed at room temperature. Directionally solidified samples showed the γ dendrite fibers formed in the Ni3Al matrix in the hypo eutectic composition of 23 at.% Al, the γ‘ single phase in the eutectic composition of 24.5 at. % Al, and the β dendrite fibers in the γ‘ matrix in the hyper eutectic compositions of 25, 26, 27 at.% Al. The hypoeutectic alloy including γ dendrites with γ‘ matrix exhibited a large elongation of over 70% with ductile transgranular fracture at room temperature. With increasing Al contents, the γ dendritic microstructure changed to the β dendrite in the γ‘ matrix, which resulted in decreasing the elongation by increasing the volume fraction of the brittle β dendrites in the ductile γ’ matrix.

Abstract: Polycrystalline samples of NiAl have been deformed in torsion in the temperature range 800K – 1300K. Deformation is accompanied by dynamic recrystallization, which with increasing temperature changes from continuous to discontinuous mode. Emphasis was put on the occurrence of continuous dynamic recrystallization, which will be discussed with respect to texture and microstructure.