Papers by Keyword: Microstructure Change

Abstract: The microstructure and hardness changes of a non-equiatomic Al₅Cr₁₂Fe₃₅Mn₂₈Ni₂₀high-entropy-alloys (HEA) with cold rolling are presented here. Using a variety of characterization methods, it is shown that the alloy is single FCC phase structure which doesn't change with cold rolling up to90%CR. With increasing the cold rolling reduction ratio, the hardness increased and the dendritic structures are broken and refined.

Abstract: The heat treatment process of a kind of hypereutectic aluminum silicon alloy which is suitable for semi-solid forming and the change of microstructure and performance during the process of heat treatment had been studied in this paper. In order to guide the heat treatment process, the phase diagram of the alloy had been calculated by the software of Thermo-Calc, and the theoretical solid and liquid line had been gotten. Twelve kinds of heat treatment process had been selected in this study. Finally the best process which the solution temperature is 495°C for 2h and aging temperature is 160°C for 8h had been gotten.

Abstract: This paper focuses on the microstructure change of bionic units, processed by the bionic laser, on vermicular cast iron, during the thermal fatigue tests. The results show that the microstructure of bionic units is uneven, and the thermal fatigue first occurs in the region with coarser microstructure on the surface of bionic units; the thermal fatigue failure mode of the bionic units is oxidizing, fracturing and peeling layer by layer.

Abstract: Fractal analysis based on results of high temperature X-ray diffraction experiment was used to study the temporal-spatial properties of particles in In-40wt.%Sn melt. Partially-overlapping multirange fractal structure is observed in In-40wt.%Sn melt, and as temperature decreases from 800°C to 130°C, low fractal dimension was found to range between 2.000 and 2.669, high fractal dimension is still 3.000 without alteration. Moreover, low fractal dimension reveals a discontinuous change between 600°C and 700°C. Fractal characteristics of In-40wt.%Sn melt were correlated with the evolution of microstructure. The discussion was made in detail. Multirange fractal model was proposed to calculate transition region curves of multirange fractals. The results show that values of simulation show good agreement with experimental values, the maximum error is less than 1.3%. From the analysis, the range of the transition region between two fractal regions is speculated to be related with structure properties of metal melts. In addition, ultrafine particles’ aggregation mechanism was used to analyze the fractal morphologies. Keywords: multirange fractal; In-40wt.%Sn melt; microstructure change; X-ray diffraction.

Abstract: Nickel-based creep resisting alloys (strengthened by γ´) are the basic materials for high-temperature constructional parts in aircraft engines and energy units. These parts are exposed to combined effects of mechanical stresses, high temperature and dioxide-corrosion conditions. The microstructure changes of cast polycrystalline Ni-based superalloy IN713LC after creep exposure were studied. Three specimens with three different diameters were used for creep tests. The degradation stage (damage parameter π) was determined for all parts of specimens. Individual parts of specimens were metallographic observed and analyzed by image analysis after rupture. The results were compared with model of stress distribution in the specimen with potential damage in the centre of the specimen.

Abstract: Substantial differences – mainly in plasticity – were found based on statistical analysis of hot rolled bars mechanical properties. Investigations presented in the paper were related to the possibility of modification of continuous bar mills used now in order to improve and stabilise plastic properties determined by the energy of breaking. The paper presents results of laboratory investigations representing processes of conventional and normalising rolling of bars from S355 steel. The experimental analysis of both rolling processes comprised assessment of actual changes occurring in the microstructure of bars, deformed acc. to suggested parameters corresponding to conventional and normalising rolling. The investigations included also the assessment of accelerated cooling after rolling influence on the microstructure of finished products.

Abstract: To estimate the ion-irradiation effect on various types of SiCf/SiC composites, a silicon self-ion irradiation was performed at temperatures of 600 °C and 1200 °C and at doses of 5 dpa and 20 dpa, respectively. These SiCf/SiC composites were prepared by different processes such as CVI (chemical vapor infiltration), WA-CVI (SiC whisker assisted CVI) and hot-pressing (HP) method. Hardness was measured by a nano-indentation tester and microstructural changes were observed by TEM with SAD(selected area diffraction) technique for the specimens prepared by FIB (Focused Ion Beam) milling. The damage dose was calculated by the SRIM2003 code and then compared with microstructureal observation.

Abstract: Single crystal superalloy TMS82+ and model alloys of Ni-12Al and Ni-6Cr-8Co-12Al were electroplated with 5-6μm of platinum and heat treated at 1000°C for up to 100hrs. In the model alloys the platinum concentration gradient in the interdiffusion region caused uphill diffusion of aluminium. The subsequent surface enrichment led to formation of aluminium-rich γ′ phase. In TMS82+ superalloy inward diffusion of platinum resulted in loss of the γ/γ′ microstructure and formation of new γ and γ′ grains. The initial dissolution of the γ′ cubes was due to the outward diffusion of aluminium. Again, the presence of a platinum gradient in the interdiffusion region resulted in uphill diffusion of aluminium and a net increase in aluminium content at the alloy surface, leading to a near-surface single-phase γ′ layer being formed, however topologically close-packed (TCP) phase formation was not observed.

Abstract: The superplastic properties of Ti3Al base alloy have been investigated in the range of 900~1020°C and strain rate range of 3.3×10-4~3.3×10-2s-1 .The largest elongation of 1570% was obtained under the optimal superplastic deformation condition of 980°C and 3.3×10-4 s-1. The m-value varied from 0.46 to 0.59, its maximum value was obtained at 980°C.The microstructure of the alloy after heat treatment was composed of two phases of small spherical α2 phase particles distributing in βtransus matrix. Microstructure change has an obvious effect on the superplastic properties of Ti3Al-based alloy. At 980°C,when theα2 phase grain size changed from large to small then large and the cavitations in the fracture surface were larger and deeper with decreasing strain rate, the alloy showed the larger elongation and the lower flow stress.