Papers by Keyword: Internal Oxidation

Abstract: Cu-Al₂O₃ alloy combine both high electronic conductivity and high softening temperature. Cu-Al₂O₃ alloy was fabricated by internal oxidation and hot extrusion methods in the present investigation. Microstructure and properties of Cu-Al₂O₃ alloy was studied. The influence of preparation parameters, hot extrusion parameters and heat treatment on the properties of the alloy was investigated. The results indicated that the grain of the alloy was very small with a size between 2-10μm. Softening temperature of the Cu-0.6% Al₂O₃ alloy and Cu-1.0% Al₂O₃ alloy was 900. Cu-0.6%Al₂O₃ alloy and Cu-1.0% Al₂O₃ alloy meeting the requirements for electrode in resistance welding is the ideal substitution of the traditional electrode materials for resistance welding.

Abstract: Internal oxidation Cu-Al alloy sheet processing has been used to prepare dispersion-strengthened Al₂O₃/Cu composites. A new technique has been developed that successfully avoids mixed Cu-Al powder preparation, H₂-reduction, and sintering processes. The microstructure and phase were investigated by metallurgical microscope, SEM, and TEM. Holding-time, internal oxidation temperature and thickness of Cu-Al alloy sheet were the three key factors with regard to preparing Al₂O₃/Cu composites by internal oxidation in Cu-Al alloy sheet. The mechanical characteristics and electric properties of Al₂O₃/Cu composites sheet and hot-extruded rod were examined. The results show hot extrusion process enhances microhardness and ultimate tensile strength to a higher level with and exerts a little influence on high electrical conductivity.

Abstract: The 1.5%Y2O3/1.5%La2O3/Cu composite was prepared by oxygen and nitrogen atomization spray deposition technique and internal oxidation. The microstructures, hardness, strength, electrical conductivity and arc erosion surface of the composite were investigated by optical light microscope, scanning electron microscope, micro-hardness tester, tensile test and arc erosion experiment. The results show that, with the increasing of internal oxidation temperature, the grains of the composite grow up obviously. When the internal oxidation reaches to 1000°C, the matrix grains begin to appear annealing twins. The micro-hardness was 436HV, the ultimate tensile strength was 580MPa, yield tensile strength was 503MPa, elongation of alloy was 8.7% and the electrical conductivity was 87% IACS of the composite by internal oxidation at 1000°C for 2h.The arc erosion surface shows a large number of paste-like coagulum and bubbles. Introduction

Abstract: Fe - 9 to 12%Cr alloys are a material for the thick sections boiler components and steam lines of a power plant. The role Fe - 9 to 12%Cr alloys is becoming more prominent in the development of a new generation of Ultra-Supercritical (USC) Power Plant due to the target operating temperature is reaching 620 °C (893 K), in 100% steam condition as well as pressure in excess of 300 bar (30 × 106 Pa). In such condition, the integrity of Fe - 9 to 12%Cr alloys relies on the oxide scale formed during the time of exposure. However due to the high temperature and water vapor condition, it is a well known fact that, the formation of oxide scale is accelerated thus depleting the structural integrity of the Fe - 9 to 12%Cr alloys over the time. Studies show that not only the formation of protective oxide scale was suppressed but the formation of non-protective oxide scale was accelerated instead. Decades of studies done by various groups around the globe has yet to have consensual on the exact mechanism of this phenomenon. Initial stage oxidation of these alloys plays great roles in hope to understand the formation of oxide scale in water vapor condition at high temperature. This paper reviews previous research works to understand the initial stage oxidation of Fe - 9 to 12%Cr alloys at high temperature in water vapor condition.

Abstract: The papers focus is to establish the criterion for the transition from internal to external oxidation. This criterion is a simple value of oxide volume fraction where the coalescence of the nodular oxide in the continuous layer is considered as inevitable. It is obtained by the Wagners analytical solution and by the data of Giggins et al. [1], which give the experimental transition from internal to external oxidation between 10 and 11 weight percent of chromium in the initial alloy. This paper also enables to obtain the oxygen diffusion coefficient in pure nickel thanks to the experimental results of oxidation at 950 °C during 10 hours on Ni-0.2Cr, Ni-1Cr and Ni-5Cr model alloys.

Abstract: Pure Ni was aluminized with an Ni₃Al, NaCl and Al₂O₃ pack powder mixture at 1100°C for 12 h. The Ni(Al) solid solution formed in aluminized Ni was internally oxidized at 1000°C for 2 to 12 h with a Co/CoO buffer. The internal oxidation zone consisted of 2 regions: granular precipitate zone near the surface and rod-like zone near the oxidation front. The growth of internal oxidation zone deviated from the parabolic law due to the non-constant Al profile developed by the aluminizing process. The granular zone grows linearly from the surface of the alloy.

Abstract: A simple metallurgical process for fabricating oxide nano-rod array structures via internal oxidation is described. Some dilute alloys such as Ni(Al) and Fe(Al) solid solutions develop rod-like oxide precipitates after their internal oxidation at high-temperatures and under low oxygen partial pressures. The oxide nano-rod array structure can be developed on the metal substrate by removing the metallic matrix of the internal oxidation zone. Al₂O₃ or MAl₂O₄ (M=Ni or Fe) spinel nano-rod array structures were prepared by using M(Al) solid solutions. Pack cementation process to develop M(Al) solid solution surface layers was used for the fabrication of nano-rod array structures on substrates with desired shape. Near-net shape Ni substrates with oxide nano-rod array structures on their surfaces can be prepared by using pack cementation and internal oxidation.

Abstract: The boundary constants between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were calculated in order to clarify the formation mechanism of fayalite scale (Fe₂SiO₄) or chromite scale (FeCr₂O₄), which can form as a “sub-scale” in Si or Cr containing steels. The diffusion coefficient of oxygen in the alloy, Do, and the oxygen concentration at the specimen surface, N_O^(s), which are constituents of the internal oxidation rate constant, (2D_ON_O^(s)/N_B^(O)n), were calculated for various oxidation conditions, and the rate equation for internal oxidation was derived. By comparing the calculated and measured values of (2D_ON_O^(s)/N_B^(O)n), we confirmed that the rate equation determined for internal oxidation was reasonable. The boundary condition between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were also calculated by substituting the calculated values of D_O and N_O^(s) into the rate equation.

Abstract: A numerical model is presented to simulate the diffusional transport of oxygen and that of an alloying element, within a 1-D binary Ni alloy, leading to the selective oxidation of the alloying element and the formation of an internal oxide precipitate. This specific model is written in MATLAB and, with the aid of the Matlab Toolbox, is coupled to the ThermoCalc extensive database. A reaction time is introduced to overcome problems related to the difficulty of formation of the internal oxide. Two cases are considered: Al as the alloying element for which the solubility product of the oxide forming elements is small, and Mn for which it is large.

Abstract: The cyclic oxidation behaviour of Ni 5.5Al 2.6Ti 4.8Co 3.9Mo 5.0W 11.0Cr superalloy at 900 °C in air has been investigated by means of measuring the kinetics curves of the oxidation and analysis method of XRD and SEM/EDAX. The results show that the mass gain rapidly increases in the initial stage, and the weight loss and mass gain occurs alternately during the cyclic oxidation. An obvious oxidation and internal oxidation occurs during cyclic oxidation. Ti in the alloy oxidized, diffusing through the Al2O3 and Cr2O3 scales to form faceted TiO2 particle on the surface of the alloy. Al2O3 formed discontinuousness inner oxides in the alloy.