Materials Science Forum Vol. 850

Abstract: Rare earth-transition metal (R-T) intermetallics have been well used because of their excellent properties. The X-ray diffraction patterns of many new phases in the R-T system have not been extensively studied. A new compound AlCrNi₃Pr was prepared by arc melting using non-consumable tungsten electrode under argon atmosphere, and then annealed at 1023K for 30 days. The X-ray powder diffraction data of AlCrNi₃Pr was collected on a Rigaku SmartLab X-ray powder diffractometer. The powder patterns of the compound were indexed, and the structure refinement by using Rietveld method indicated that the AlCrNi₃Pr compound crystallized in the hexagonal structure, space group P6/mmm (No.191) with PrNi₅ structure type, a=b=5.0553(9) Ǻ, c=4.0763(6) Ǻ, V=90.22Ǻ³, Z=1, ρ_x=7.288g cm^-3, the Smith–Snyder FOM F₃₀=279.1(0.0044, 32) and the intensity ratio RIR=1.23.

Abstract: A new Al-Cu-Nd system alloy, the high-purity Al₂Cu₃Nd ternary compound, was developed and prepared with the stoichiometric amounts of elemental constituents by arc melting under argon atmosphere. The X-ray diffraction (XRD) data of Al₂Cu₃Nd was collected by using the Rigaku Smart Lab X-ray powder diffractometer, and all X-ray diffraction peaks of Al₂Cu₃Nd compound were indexed successfully with the hexagonal structure. The Rietveld refinement results of the XRD pattern for the Al₂Cu₃Nd compound showed that the Al₂Cu₃Nd compound is the hexagonal structure, space group P6/mmm (No.191) with a = 5.2397(1) Å, c = 4.1783(1) Å, V = 99.34 ų, Z = 1. The density of the compound was 6.501 g/cm³, and its reference intensity ratio (RIR) w 1.26.

Abstract: The dynamic recrystallization behavior of 18 Ni maraging steels was investigated by hot compression tests at temperatures ranging from 900 °C to 1100 °C and strain rates ranging from 0.001 to 1 s^-1. Based on the flow curves from the tests, the effects of temperatures and strain rates on the dynamic recrystallization behavior were analyzed. The strain-hardening rates versus stress curves were used to determine to the critical strain, the peak stress (strain), the saturated stress and the steady stress. With the assistance of the process parameters, constitutive equations were obtained and the activation energy was determined to be 413544.96 J/mol. The dependence of the characteristic values on Zener-Hollomon was found. The dynamic recrystallization kinetics model of the tested steels was constructed and the validity was confirmed based on the experimental results.

Abstract: In this work, eleven Mn-La alloys were investigated experimentally by means of thermal analysis. The temperatures of the invariant reactions in the Mn-La binary system were determined. To confirm whether the liquid miscibility gap exists in the Mn-La system, one key alloy (Mn₇₂La₂₈) was prepared and then checked by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). Microstructure observation and composition analysis indicated the nonexistence of the liquid miscibility gap. Based on the experimental results obtained in the present work and the critical review of the available experimental data in the published literature, a set of self-consistent thermodynamic parameters for the Mn-La system was obtained using the CALPHAD method by thermodynamic optimization of the selected experimental data.

Abstract: As the key sub-binary systems in the rare-earth (RE) permanent magnetic materials with excellent magnetic properties (e.g. Nd-Fe-B, Sm-Fe-N magnets), the Fe-RE binary systems were investigated widely due to the industrial applications of permanent magnets. In this work, the experimental data of phase equilibria and thermodynamic properties of the Fe-RE binary systems (RE=La, Ce, Pr, Nd) in the published literature are reviewed firstly. Based on available phase equilibria data and thermodynamic data, the Fe-RE binary systems are assessed thermodynamically using the CALPHAD method. As a result, further experimental information and thermodynamic calculations will be both required in order to develop thermodynamic database of the RE-Fe-B ternary systems, which is very useful to study the relations between alloy composition, microstructure and magnetic properties of novel Nd-Fe-B-based permanent magnets.

Abstract: The deformation characteristics of pure copper have been investigated by compression tests in the temperature range of 20 °C~900 °C and strain rate range of 0.001 s^-1~1 s^-1. The results showed that the flow stress of pure copper increased with increasing strain rate and decreasing deformation temperature. Three types of strain-contained flow stress prediction models were developed. The flow stress prediction models based on parameters such as α, Q, lnA and n were related to deformation temperature, strain rate and strain, the prediction accuracy of the flow stress was deeply influenced by the cumulative error of multi-parameter fitting. The flow stress prediction model based on σ, , ε and T constitutive relations and the flow stress prediction model based on GA+BP possessed less correlation with microscopic deformation mechanism, proving to have high prediction accuracy, in which GA+ BP-based flow stress prediction model is in very good agreement with true stress curve, which is of significance to the guidance of hot working of pure copper.

Abstract: Reactor pressurized vessel (RPV), which determines the lifetime of the nuclear power plant (NPP), is mainly forged using A508-3 steel in China. In order to meet the requirement of the small specimen test technique in the nuclear application, the fracture toughness of A508-3 steel was tested under-100°C using 1/4 CT specimens, and analyzed using Master Curve according to ASTM E 1921. In this work, the relationship of the K_IC and the distance between the cleavage crack initiation site and the front of the fatigue crack is studied, and the transition temperature T₀ of A508-3 is-98.7 ^oC, which is quite close to the test temperature.

Abstract: Plastic deformation and recrystallization of a Ni-based single crystal superalloy were experimentally investigated. Compression and Brinell Indentation were utilized to cause plastic deformation, and thereafter some deformed samples received heat treatment. Surface topography around the indent confirms the anisotropic plasticity of single crystal superalloys. The influential distance below the indent is much larger than that on the indent surface. Microstructural observation by Electron Back-scatter Diffraction (EBSD) shows that it is easier for nucleation and grain boundary migration in the dendritic arms. In addition, the recovery has almost no effect on preventing recrystallization for deformed samples with small plastic strains (around 5%).

Abstract: Since gas turbine blades in engines suffer centrifugal stress and gas corrosion during service, a good creep resistance in hot corrosion environment is one of the important considerations to evaluate service performance of the blade materials. In this work, the creep rupture behaviors of the directionally solidified superalloy DZ466 with and without salt deposition at 760°C/765MPa, 850°C/500MPa and 950°C/220MPa are preliminarily investigated based on the creep properties measurement and microstructure observations. The effects of hot corrosion on the creep properties and fracture mode are examined. The results show that the creep-rupture life in salt-deposit environment is lower than that in air-exposure environment at different temperatures. The creep-rupture life reduction caused by hot corrosion is increased with increase of the creep temperature. The fracture mode is exhibited by transgranular fracture in all crepted specimens. The propagation directions of all the secondary cracks are almost perpendicular to the crept specimen surface or the stress axis. The surface cracks are mainly produced in air-exposure environment at low temperature or in salt-deposited environment at high temperature. Induced by the stress concentration, the internal cracks are initiated surrounding the carbides in both air-exposure and salt-deposit environments. The creep-rupture life is dependent on the crack initiation at low temperature but on the crack propagation at high temperature. The reduction of the active load bearing area in transversal direction is the main reason why the creep-rupture life is decreased at 950°C.