Si Cr Ni Alloy Research Articles

Rare earth application for heat-resisting alloys

High-temperature oxidation resistance of Al 2O 3- and Cr 2O 3-forming heat-resisting alloys with rare earths (yttrium-implanted FeCrAl, -added FeCrAl, -added FeCrAlPt alloys, Y 2O 3- or CeO 2-coated NiCrSi, yttrium- or lutetium-added NiCr and NiCrSi) was studied in oxygen at high temperatures, by mass gain measurements, mass change measurements, amount of spalled oxide, observation of surface appearance, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe X-ray microanalysis (EPMA) and transmission electron microscopy (TEM). After oxidation at 1573 K for 18 ks in oxygen, oxide scale on FeCrAl alloy spalled from the entire surface, however, yttrium-implanted FeCrAl alloys showed good oxide adherence. After oxidation at 1473 K for 18 ks in oxygen, mass gain of FeCrAlY alloys decreased with increasing yttrium of up to 0.1 wt.% follwed by an increase with the yttrium content, and the mass gain of FeCrAl0.005Pt0.05Y alloy with appropriate additions of platinum and yttrium was lower than that of FeCrAl0.1Y alloy. Yttrium-added FeCrAl alloys showed good oxide adherence. TEM analysis revealed that the alumina/alloy interface of FeCrAl0.005Pt0.05Y alloy showed good coherency. The scale surface of FeCrAl alloy was rough, however, those of FeCrAlY and FeCrAlPtY alloys were smooth. Cyclic oxidation of NiCrSi, Y 2O 3- or CeO 2-coated NiCrSi alloys was studied up to 10 cycles (1 cycle: 300 s) at 1523 K in oxygen. Mass change of NiCrSi alloy increased up to 3 cycles and then decreased up to 10 cycles because of oxide spallation during cooling. On the other hand, mass change of Y 2O 3- or CeO 2-coated NiCrSi alloy increased up to 10 cycles, and these alloys showed good oxide adherence. Granular Cr 2O 3 particles on Y 2O 3-coated NiCrSi alloy were in size smaller than these on CeO 2-coated NiCrSi alloy. This result suggested that oxidation rate of Y 2O 3-coated NiCrSi alloy was lower than that of CeO 2-coated NiCrSi alloy. After oxidation at 1473 and 1573 K for 18 ks in oxygen, mass gain of yttrium- or lutetium-added NiCr and NiCrSi alloys decreased. Oxide scales on NiCrSi alloy markedly spalled along with alloy grain boundaries during cooling. On the other hand, yttrium- or lutetium-added NiCrSi alloys showed good oxide adherence. Granular Cr 2O 3 particles on yttrium- or lutetium-added NiCr and NiCrSi alloys decreased in size with increasing yttrium or lutetium, and increased with increasing oxidation temperature.

Thermodynamic modelling of wetting in a B4C/Ni–Cr–Si system

Wetting of ceramics by liquid metals is of significant importance in many processes. In this paper, via a thermodynamic modelling of the reactions at a ceramic–metal interface, the wetting behaviour of B4C was studied with a series of Ni–Cr–Si alloys. The thermodynamic calculations showed that the Ni–Cr–Si alloys with Ni/Cr ratio of 3.4 would react with and wet B4C ceramics at 1220 °C under vacuum conditions. Experimental verification using the sessile-drop method was performed to confirm the validity of the calculations and the assumptions made in the wetting model. In the situation where the growth rate of the reaction product was not greater than the spreading rate of the liquid, good agreement was found between the theoretical calculations and experimental data. It was also revealed that the increase in Si content in the alloys plays a major role in the improvement of wetting of B4C by Ni–Cr–Si alloys.

Study of interface interactions in B4C/Ni–Cr–Si system

Boron carbide is a ceramic material possessing unique properties, and hence, high technological applications. The wetting behavior of ceramics by liquid alloys, which is of crucial importance in a variety of materials processing technologies, is determined by interfacial chemical interactions. In the present paper, the interfacial interactions of B4C with a series of Ni–Cr–Si alloys with Ni/Cr=3.4 have been studied. For this purpose, a thermodynamic method was developed to predict the interactions. In addition, the interfacial structure and chemical composition were examined using SEM-EDS technique. Good agreement was found between the theoretical calculations and experimental data. It was revealed that the amount of Si content in the alloys plays a major role on the interfacial reactions as well as the interface microstructure.

Thermodynamic modelling of wetting at silicon nitride/NiCrSi alloy interfaces

Through thermodynamic modelling of the reaction at ceramic-metal interface, wetting of a sintered silicon nitride was investigated with a series of Ni-based brazing alloys without addition of active elements. The thermodynamic calculations showed that NiCrSi alloys with Ni/Cr ratio of 3.5 and X Si < 0.25 will react with and wet Si 3N 4 ceramics at 1220 °C (1493 K) and P N 2 = 15 Pa. Environment verifications using sessile drop method confirmed the validity of the calculations and the assumptions made in the wetting model.

Melting behaviour of nickel—chromium—silicon alloys

With regard to developing low melting NiCrSi alloys used as joint materials in high temperature brazing technics, especially in reactor technique, the melting behaviour of nickel—rich NiCrSi alloys was investigated systematically by differential thermal analysis. The dependence of the liquidus temperatures on alloying concentration ranges from 0 to 28 at. -% Si and 0 to 60 at.-% Cr shows a ternary eutectic melting temperature minimum of 1077°C at 20 at.-% Cr and 21.3 at.-% Si. The melting behaviour of the alloys in the indicated concentration range will be characterized in a reaction scheme. The dependence on temperature of the solubility of Si and Cr in Ni will be discussed.