Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： Sputtering targets of CIGS quaternary ceramic were fabricated by hot-press sintering the milled powder mixture of Cu2Se, In2Se3 and Ga2Se3. When the milling time of the powders less than 4 h, the sintered targets delaminated, while the delamination disappeared with the prolonging milling time. Therefore the physico-chemical changes of the powder mixture during the milling process and their influence on the delamination of the targets were investigated. The results indicate that with the progress of the milling process, mechanical alloying (MA) occurred, and chalcopyrite Cu(In, Ga)Se2 (CIGS) formed from Cu2Se, In2Se3 and Ga2Se3; With the increasing milling time, CuInSe2 (CIS) formed on the surface of binary copper selenide firstly and CIGS was subsequently generated due to the inward diffusion of Ga; Thus the original blend powders became a mixture of CIGS and residual Ga2Se3 after milling for 48 h. Since CIGS and Cu2-xSe have a similar crystallographic structure, therefore this epitaxial relation may facilitate the formation of CIGS. The disappearance of Cu-Se binary compound and the formation of CIGS restrained the delamination of the CIGS targets in the sintering process.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Alloy solidification is an important process to control the mechanical properties of engineering products. During solidification, dendrite fragmentation occurs commonly as a key phenomenon to determine the microstructure and to obtain fine grain size. Recently, in situ synchrotron X-radiography technique was developed and applied to observe thermodynamic behaviors such as dendrite growth and fragmentation during solidification. External forces such as mechanical and electromagnetic stirring, and thermal shock were added into the solidification process to investigate their effects on the fragmentation behavior. However, most work conducted in literature focused on qualitative aspects e.g. morphology transition or solute distribution and quantitative investigation such as determining the specific relationship between fragmentation and solidification conditions was rather limited. In this work, the third generation synchrotron X-radiography technique was used to observe the solidification process of an Al-15%Cu (mass fraction) alloy. Experimental conditions including the strength of the pulsed electromagnetic fields, dendrite growth direction and the temperature gradients were varied and the subsequent effect on fragmentation was studied and quantified. A computer program was developed based on Matlab to perform the image processing and measurement. The fragmentation number according to experiments was counted and correlated to the mushy zone depth and local solid fraction. Results showed that a stronger electromagnetic field, growing against gravity and growing at higher velocity would significantly increase the fragmentation number. Furthermore, the fragmentation number followed a Gauss distribution as a function of either mushy zone depth or local solid fraction, and the maximum fragmentation occurred when the solid fraction was about 0.45. In the end, the extent to which caused those statistic results above were analyzed as the necking process due to the velocity field, the cumulative solid due to the gravity field and the liquid flow due to the electromagnetic field.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： A 2D inverse heat transfer model between molten metal and shot sleeve was based on the nonlinear estimation method. Die casting experiments under both non-shot and shot conditions (via the plunger) were performed using an Al-9%Si-3%Cu alloy. Based on the temperature measurements from thermocouples embedded inside the shot sleeve, the temperature distribution of molten metal and interfacial heat transfer coefficient (IHTC) were successfully determined. Results show that the heat transfer behavior of non- shot condition was different from that in the shot condition, but the IHTC in the middle zone of shot sleeve decreased along the plunger moving direction. Besides, the surface temperature of shot sleeve was higher in both pouring zone and end zone while lower in the middle zone. In accordance to the movement of the plunger, the IHTC profile in the end zone exhibited double peaks.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Copper die-casting die steel is usually used in severe rugged environment. Liquid metal flows with high temperature and high pressure during injection and provides rapid filling of the die cavity. The copper die-casting steel should has excellent combination of the properties of high toughness, wear resistance, hardness, thermal fatigue resistance, oxidation resistance and corrosion resistance at high temperature for the cavity surface of diecasting die suffers high pressure, scour, erosion and thermal shock. A new kind of copper alloy die-casting die steel with pure austenitic matrix was conducted in this work, wherein the boride with high thermal stability and high hardness distributes in the austenitic matrix. The mechanical properties of copper alloy die-casting die steel at high temperature of 850 ℃ were studied using dynamic thermal-mechanical simulation testing machine. The thermal fa-tigue behavior of die steel at room temperature to 800 ℃ was performed using self-restraint Uddeholm thermal fatigue test method, and the depth extension status of surface thermal fatigue cracks and cross-sectional cracks in die steel thermal fatigue specimens was measured using stereo microscope and SEM. The effects of B content on the mechanical properties at room temperature and high temperature and on the thermal fatigue resistance were evaluated. The experimental results showed that boride distributes in austenitic matrix in the form of M2B-type boride (M represents Fe, Cr or Mn) after adding B in the tested steels, and the comprehensive performances of steel at high temperatures were effectively improved, the hardness of the steel at room temperature increased from 200 HV to 302 HV, the tensile yield strength at 850 ℃ increased from 144.3 MPa to 190.3 MPa, and the compressive yield strength increased from 139.7 MPa to 167.9 MPa. Evaluation of the degree of heat checking on 300 cyc of thermal fatigue testing at room temperature to 800 ℃ showed that the die steel containing B was rating 2~3, much better than rating 7~8 of electroslag remelting ESR-H13 steel for comparison, which mainly because the thermal fatigue cracks were blunted or deflected by boride, and then the cracks spread as scattering shapes was avoided.
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