Papers by Keyword: Ni-Cr Alloy

Abstract: Industrial pure aluminum has been widely used in industry. However, it caused great difficulties in welding process due to its characteristics such as easy oxidation, high thermal conductivity and specific volume, low melting point. In order to overcome this problem, improving the welding quality of industrial pure and reducing the welding defects is of great significance. In this paper, the weldability of 1050A industrial pure aluminum plate (5 mm thick) with HS331, SAl-2, 1050A leftover materials and homemade welding wire with Ni-Cr alloy as four different filler materials was studied by using manual TIG welding. Metallographic test and mechanical performance test were used to assess microstructure and mechanical properties of the resulting welding joint. The results show that the microstructure and mechanical properties of the resulting welding joint with homemade welding wire with Ni-Cr alloy is relatively better than the others, which offers important implication for the improvement of the welding properties of industrial pure aluminum.

Abstract: This study evaluated the microstructure and mechanical properties enhancement of cross roll rolled Ni-10Cr alloy, comparing with conventional rolled material. Cold rolling was carried out to 90% thickness reduction and subsequently annealed at 700 °C for 30 min to obtain the fully recrystallized microstructure. Particularly, cross roll rolling was carried out at a tilted roll mill condition of 5º from the transverse direction in RD – TD plane. Application of cross roll rolling on Ni-10Cr alloy contributed to the notable grain refinement due to higher effective strain than that of conventional rolling, consequently, average grain size was refined from 135 µm in initial material to 4.2 µm in cross roll rolled material. Furthermore, //ND texture in CRR material was well developed than that of CR material, which contributed to the mechanical properties and formability enhancement.

Abstract: This study evaluated the microstructure and mechanical properties enhancement of cross roll rolled Ni-10Cr alloy, comparing with conventional rolled material. Cold rolling was carried out to 90% thickness reduction and subsequently annealed at 700 °C for 30 min to obtain the fully recrystallized microstructure. For annealed materials after rolling, to investigate the grain boundary characteristic distributions, electron back-scattering diffraction technique was introduced. Application of cross roll rolling on Ni-10Cr alloy contributed to the notable grain refinement, consequently, average grain size was refined from 135 μm in initial material to 4.2 μm in cross roll rolled material. These refined grain size led to an enhanced mechanical properties such as yield and tensile strengths. Furthermore, <111>//ND texture in CRR material was well developed than that of CR material, which contributed to the mechanical properties and formability enhancement.

Abstract: Samples of high temperature brazing diamond with Ni-Cr alloy are prepared in protective atmosphere furnace for brazing time is 1 minute, 2 minutes, and 5 minutes. The microstructures were analyzed with Scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The results show that there are two layers of carbides on the surface of diamond, lamellar carbide Cr3C2 and columnar carbide Cr7C3, the growth direction of Cr3C2 has a certain orientation relationship with the crystallographic plane of diamond, and Cr7C3 nucleates on the surface of Cr3C2. With the increase of brazing time, the morphology of carbide Cr3C2 turns from linear to lamellar and carbide Cr7C3 turns from granule to columnar. After brazing, chemical metallurgical combination is achieved between diamonds and brazing alloy and carbides are the primary reason for the strong bond strength.

Abstract: The performance of Ni-based alloys at high temperature strongly depends on the formation of a protective chromia scale which prevents from fast growth NiO scale. The evolution of the oxide scales will be shown to be strongly dependent on the chromium content especially for the shortest oxidation times. Indeed, transient stages will be reported to condition the subsequent oxidation behavior at longer times until the oxidation rate constant becomes invariant. To this end, a comparative study on the outward and inward diffusion of species upon oxidation at 800°C for short times (0.5 / 1 / 2 / 4 / 8 h) has been evaluated on commercial available Ni20Cr and Ni30Cr alloys through in-situ Raman spectroscopy and supported by post-mortem X-ray diffraction (XRD) as well as scanning electron microscopy coupled to energy dispersive spectrometry (FEG-ESEM / EDS) investigations.

Abstract: Precision fit of dental prostheses were compared between the four experimental groups of cast Ni-Cr alloy, cast titanium, milled titanium and milled zirconium by measuring and comparing the mean values of the marginal, axial, occlusal and overall coping-die gaps. The overall, axial and occlusal fit was most precise with the cast Ni-Cr alloy prosthesis. The biologically critical marginal fit was the most precise with the milled zirconium, thus suggesting that the copy-milled zirconia ceramic could serve as an alternative to the cast-metal prosthesis. The statistical variables, such as the groups and the regions, were in association with and had an interaction effect on the adaptability of the prostheses. The marginal gaps correlated with the axial gaps in the cast Ni-Cr alloy and milled titanium groups

Abstract: To suppress interdiffusion between the coating and alloy substrate in addition to ensuring slow oxide growth at very high temperatures advanced coatings were developed, and they were classified into four groups, (1) the diffusion barrier coating with a duplex layer structure, an inner σ−(Re-Cr-Ni) phase as a diffusion barrier and outer Ni aluminides as an aluminum reservoir formed on a Ni based superalloy, Hastelloy X, and Nb-based alloy. (2) the up-hill diffusion coating with a duplex layer structure, an inner TiAl2 + L12 and an outer β-NiAl formed on TiAl intermetallic and Ti-based heat resistant alloys by the Ni-plating followed by high Al-activity pack cementation. (3) the chemical barrier coating with a duplex layer structure, an inner* γ + β + Laves three phases mixture as a chemical diffusion barrier and an outer Al-rich γ-TiAl as an Al reservoir formed by the two step Cr / Al pack process. (4) the self-formed coating with the duplex structure, an inner α-Cr layer as a diffusion barrier and an outer β-NiAl as an Al-reservoir on Ni-(20
50)at% Cr alloy changed from the δ-Ni2Al3 coating during oxidation at high temperature. The oxidation properties of the coated alloys were investigated at temperatures between 1173 and 1573K in air for up to 1,000 hrs (10,000 hrs for the up-hill diffusion coating). In the diffusion barrier coating the Re-Cr-Ni alloy layer was stable, existing between the Ni-based superalloy (or Hastelloy X) and Ni aluminides containing 12
50at%Al when oxidized at 1423K for up to 1800ks. It was found that the Re-Cr-Ni alloy layer acts as a diffusion barrier for both the inward diffusion of Al and outward diffusion of alloying elements in the alloy substrate. In the chemical barrier coating both the TiAl2 outermost and Al-rich γ-TiAl outer layers maintained high Al contents, forming a protective Al2O3 scale, and it seems that the inner, γ, β, Laves three phase mixture layer suppresses mutual diffusion between the alloy substrate and the outer/outermost layers.