Search

In order to study the effect of the rolling process and aging on the microstructure evolution and mechanical and tribological properties of the material, room-temperature rolling (RTR), cryogenic rolling (CR), and deep cryogenic treatment after rolling (RTR + DCT) experiments were carried out on a Cu-1.0Cr-0.1Zr alloy by a large plastic deformation process. Alloy plates were aged at 550 °C for 60 min. Different rolling processes and aging treatments have different effects on the microstructure and properties of alloy plates. The alloy plate is rolled and deformed, and the grains change from equiaxed to layered. Compared with RTR and RTR + DCT treatment, CR can promote the precipitation of the Cr phase and the degree of grain fragmentation is greater. After aging treatment, the Cu-Zr mesophase compounds in the microstructure increased, the alloys treated with CR and RTR + DCT appeared to be partially recrystallized, and the number of twins in the CR alloy plate was significantly more than that of RTR + DCT. The ultimate tensile strength of the alloy plate reached 553 MPa and the hardness reached 170 HV after cryogenic rolling with 90% deformation, which indicates that CR treatment can further improve the physical properties of the alloy plate. After aging at 550 °C for 60 min, the RTR 90% + DCT alloy plate has a tensile strength of 498 MPa and an elongation of 47.9%, which is three times that of the as-rolled alloy plate. From the research on the tribological properties of alloy plates, we learned that the main wear mechanisms in the wear forms of CR and RTR + DCT alloy plates are adhesive wear and abrasive wear. Adhesive wear is dominant in the early stage, while abrasive wear is the dominant mechanism in the later stage of wear. The friction coefficient of the CR 90% alloy plate in the TD direction is close to 0.55, and the wear rate is 2.9 × 10−4 mm3/Nm, indicating that the CR treatment further improves the wear resistance of the alloy plates. [ABSTRACT FROM AUTHOR]

Three powder metallurgical Ti-48Al-2Cr-2Nb compacts were prepared using spherical pre-alloyed powders, mechanically milled powders, and a mixture of the spherical pre-alloyed powders and the mechanical milled powders in a weight ratio of 1:4. Different microstructures corresponding to coarse grains, ultrafine grains, and bimodal-size grains, respectively, were obtained. The compact with a bimodal grain structure exhibits a good combination of high-yield compressive strength (~ 1393 MPa) and improved compression ratio to fracture (~ 13.9%) at room temperature due to the effects of back-stress and ductile γ-TiAl single-phase layer generated near the ultrafine/coarse grain interface. At high temperatures, the compressive properties of the compact with the bimodal grain size distribution are sensitive to the temperature. A relatively high deformation resistance is achieved at 750 °C. At this temperature, the coarse grain region of the bimodal grain-sized microstructure undergoes more strain, and the dynamic recrystallization is promoted with increasing strain, improving the ductility. By contrast, the ultrafine grains in the bimodal grain size microstructure dominate the dynamic softening when the temperature is higher than 850 °C due to their accelerated dynamic recrystallization and easy grain boundary slip that are responsible for the good formability and the sharp decrease in deformation resistance of this alloy. [ABSTRACT FROM AUTHOR]

Background and aims: Patient satisfaction is one of the important ways to measure the results of treatment and the quality of medical services. The purpose of the present study was to verify the reliability and validity of the indicator system for evaluating satisfaction of outpatients and inpatients in Chinese hospitals.Methods: The study was based on the satisfaction questionnaire program of the national doctor–patient experience research center with data from 99,802 outpatients and 229,215 inpatients, collected in China between 2016 and 2017. We adopted exploratory factor analysis for validity analysis and the method of split-half reliability and Cronbach's α coefficient for reliability analysis.Results: In the validity analysis of the indicator system for outpatients, the factor loading was between 0.438 and 0.919, and the reliability was excellent. In the validity analysis of the indicator system for nonsurgical inpatients, the factor loading of the secondary indicators was between 0.417 and 0.75, and the reliability was excellent. In the validity analysis of the indicator system for surgical inpatients satisfaction, the factor loading of the secondary indicators range was 0.391–0.751, and the reliability was excellent.Conclusion: The indicator systems for evaluating satisfaction of outpatients, surgical inpatients and nonsurgical inpatients all have excellent reliability and good validity. They can be widely used for an outpatient and inpatient satisfaction questionnaire in Chinese hospitals. [ABSTRACT FROM AUTHOR]

This paper investigated the microstructure transformation behavior of copper–graphite composites prepared via mechanical alloying/ spark plasma sintering (MA-SPS). The results revealed that the composite powder existed in the forms of nano/submicron composite particles and pure nanoparticles. The composite particles were totally bonded together via the MA-SPS process and showed a dense and fine microstructure. The grain shape was different from that of the milled powder particles. The microhardness values of Cu–9.7 at.% C, Cu–18.1 at.% C, and Cu–25.3 at.% C composites were enhanced greatly compared with pure copper. The enhancement is due to the combination of the MA induced by high-energy ball milling from MA and discharge activation induced by pulsed current discharge from SPS in the MA-SPS fabrication process. [ABSTRACT FROM AUTHOR]

Duplex stainless steel composites with various weight fractions of TiC particles are prepared by spark plasma sintering. Ferritic 434L and austenitic 316L stainless steel powders are premixed in a 50:50 weight ratio and added with 3-9 wt.% TiC. The compacts are sintered in the solid state under vacuum conditions at 1223 K for 5 min. The effects of TiC content on the microstructure, hardness, and corrosion resistance of duplex stainless steel composites fabricated by powder metallurgy are evaluated. The results indicate that the TiC particulates as reinforcements can be distributed homogeneously in the steel matrix. Densification of sintered composites decreases with increasing TiC content. MC carbide precipitates along grain boundary, and its neighboring Cr-Mo-depleted region is formed in the sintered microstructure, which can be eliminated subsequently with appropriate heat treatment. With the addition of TiC, the hardness of duplex stainless steel fabricated by powder metallurgy can be markedly enhanced despite increased porosity in the composites. However, TiC particles increase the corrosion rate and degrade the passivation capability, particularly for the composite with TiC content higher than 6 wt.%. Weakened metallurgical bonding in the composite with high TiC content provides the preferred sites for pitting nucleation and/or dissolution. [ABSTRACT FROM AUTHOR]

Cu-2.4 wt.%V nanocomposite has been prepared by mechanical alloy and vacuum hot-pressed sintering technology. The composites were sintered at 800 °C, 850 °C, 900 °C, and 950 °C respectively. The microstructure and properties of composites were investigated. The results show that the Cu-2.4 wt.%V composite presents high strength and high electrical conductivity. The composite sintered at 900 °C has a microhardness of 205 HV, a yield strength of 404.41 MPa, and an electrical conductivity of 79.5% International Annealed Copper Standard (IACS); the microhardness and yield strength reduce gradually with the increasing consolidation temperature, which is mainly due to the growth of copper grain size. After sintering, copper grain size and V nanoparticle both maintain in nanoscale; the strengthening mechanism is related to grain boundary strengthening and dispersion strengthening, while the grain boundary strengthening mechanism plays the most important role. This study indicates that the addition of small amounts of V element could enhance the copper matrix markedly with the little sacrifice of electrical conductivity. [ABSTRACT FROM AUTHOR]

In this study, dysprosium-aluminosilicate (DAS) and neodymium-aluminosilicate (NAS) glasses with high softening temperature were used as fillers to join alumina ceramics. The similarities and differences in the interfacial microstructure and flexural strength of the joints were investigated. Results showed that the glass fillers both could infiltrate into alumina ceramics during the joining process. However, excessive infiltration at high joining temperatures led to the formation of pore defects in the brazing seam. An interfacial reaction layer composed of Dy 3 Al 5 O 12 was formed at the DAS glass/alumina interface. In contrast, no interfacial reaction was observed between the NAS glass and alumina ceramic. Slower cooling rate promoted the crystallization of Dy 2 Si 2 O 7 and Al 2 O 3 in the Al 2 O 3 /DAS/Al 2 O 3 joints, and only Nd 2 Si 2 O 7 in the Al 2 O 3 /NAS/Al 2 O 3 joints. The flexural strength at room temperature of both joints first increased and then decreased with the increased of joining temperature, and showed a declined tendency with the decrease in cooling rate. The flexural strength at 900 °C of Al 2 O 3 /DAS/Al 2 O 3 joints reached 245 MPa, which is higher than that of Al 2 O 3 /NAS/Al 2 O 3 joints. [ABSTRACT FROM AUTHOR]

Transparent MgAl 2 O 4 ceramics were bonded by using CaO-Al 2 O 3 -SiO 2 (CAS) glass filler. The CAS glass filler exhibited the same thermal expansion behavior as MgAl 2 O 4 ceramic and excellent wetting ability on the surface of MgAl 2 O 4 ceramic. When the cooling rate of 15 °C/min was used, no interfacial reaction was observed and the amorphous brazing seam could be obtained. However, low joining temperature (1250 °C) led to the formation of pores and high joining temperature (1400 °C) resulted in the formation of cracks. Furthermore, the slow cooling rate of 5–10 °C/min induced the crystallization of CaAl 2 Si 2 O 8 and Mg 2 Al 4 Si 5 O 18 due to the dissolution of MgAl 2 O 4 substrate. The optimal flexural strength of 181–189 MPa was obtained when the joining temperature and cooling rate were 1300–1350 °C and 15 °C/min respectively. Moreover, the in-line transmittance of the joint at 1000 nm was 82.1%, which was slightly lower than that of MgAl 2 O 4 ceramic (85.6%). [ABSTRACT FROM AUTHOR]

In this study, an AlSi10Cu4Mg alloy was prepared by selective laser melting (SLM) using a mixture of pre-alloyed AlSi10Mg and elemental Cu powders, followed by aging at 180 ℃ for 2 h. The high-temperature tensile properties of both the SLMed and SLM-aged samples were tested in the temperature range of 200–400 ℃, and the microstructure changes during deformation were compared. At the temperature of 200 ℃, the SLMed sample exhibits outstanding tensile properties with an ultimate tensile strength (UTS) of 327±2 MPa and an elongation (EL) of 25.5±0.5 %. This is mainly related to the strain hardening that caused by the accumulation of anomalous dislocations near the high-volume fraction of Si nano-particles within the grains. For the SLM-aged sample, the aging treatment is found to further increase the strength, yielding a UTS of 381±3 MPa. The metastable transition of the Al 2 Cu phase indirectly promotes the precipitation of the nano-sized Si phase during the aging process. As the testing temperature increases, the strength increment of the SLM-aged sample gradually diminishes, while the elongation increment increases. Due to the limited intrinsic thermal stability of Si nano-particles and θ′ phase, the coarsening of the precipitates can weaken the strengthening effect. The dynamic recrystallization process can be accelerated by the aging treatment, thereby helping to improve the elongation. [Display omitted] • The high-temperature tensile properties of AlSi10Cu4Mg alloy prepared by SLM were evaluated. • The SLMed AlSi10Cu4Mg alloy exhibited outstanding comprehensive tensile properties at 200 ℃. • The metastable transition of the Al 2 Cu phase facilitates nano-sized Si precipitation during aging process. • The strength increment of SLM-aged sample gradually diminishes with increasing testing temperature while the elongation increment increases instead. [ABSTRACT FROM AUTHOR]

In this paper, a novel Dy 2 O 3 -Al 2 O 3 -SiO 2 (DAS) glass ceramic was designed and prepared for joining zirconia toughened alumina (ZTA) ceramic. The crystallization, thermal expansion behavior and wetting behavior of the DAS glass filler were studied. The effect of cooling rate and joining temperature on the microstructure and flexural strength of joints was investigated. The results show that slow cooling rate (15 °C/min) leads to crystallization of brazing seam, which causes the formation of pores in the joints due to the large density difference between the glass and the crystalline phases. The dissolution of ZrO 2 from ZTA substrate into the filler during joining process improves the mismatch of the coefficient of thermal expansion (CTE) between the brazing seam and substrate. The maximum flexural strength of 535 MPa is obtained when the joining temperature and cooling rate are 1475 °C and 50 °C/min, respectively. [ABSTRACT FROM AUTHOR]

In the present work, wetting behaviour of Ag–Cu eutectic filler on high nitrogen austenitic stainless steel (HNS) and 316L austenitic stainless steel (316L) base metals was firstly studied using a sessile drop method in high vacuum. The Ag–Cu eutectic filler exhibits completely different dynamic wetting process on the surface of HNS and 316L. The equilibrium contact angle of Ag–Cu/HNS system is lower and its wetting time is shorter than that of Ag–Cu/316L system. Subsequently, brazing experiments were carried out for HNS and 316L base metals using the same filler at 840 °C for a holding period of 5–30 min under high vacuum. Microstructural analysis shows that the 316L/316L joints are composed of α-Cu and fine Ag–Cu eutectic. The HNS/HNS joints consist of β-Ag and coarse Ag–Cu eutectic. The optimal shear strength of HNS/HNS joints (290 MPa) is significantly higher than that of 316L/316L joints (175 MPa) because of the formation of diffusion layer. Therefore, HNS has tremendous potential to take the place of the traditional austenitic stainless steels for industry application. • HNS is used to take place of traditional austenitic stainless steel for improving the wettability of Ag–Cu filler. • The Ag–Cu/HNS system shows lower equilibrium contact angle and shorter wetting time compared with the Ag–Cu/316L system. • The dissolution of Mn from HNS into filler is helpful for improving the wetting and spreading ability of Ag–Cu filler. • The optimal shear strength of HNS/HNS joints (290 MPa) is significantly higher than that of 316L/316L joints (175 MPa). [ABSTRACT FROM AUTHOR]

In this work, S30432 steel containing trace TiC/TiB 2 nano-particles was manufactured, and the effects of TiC/TiB 2 nano-particles on the microstructure and room and high-temperature mechanical properties of the S30432 steel were investigated. The addition of trace TiC/TiB 2 nano-particles can reduce the grain size from 19 ± 2.3 μm to 13 ± 4.5 μm. This is because the nano-particles provide efficient nucleation sites and constrain dendrite growth. Trace nano-particles can simultaneously enhance the strength and plasticity of the S30432 steel at room temperature. At high temperature of 600 °C, the S30432 steel with trace TiC/TiB 2 nano-particles can still maintain high strength and plasticity. However, as the ambient temperature increases, the strength increment of the S30432 steel with trace TiC/TiB 2 nano-particles decreases gradually, while the elongation increment significantly increases. The dynamic recrystallization process is promoted by the addition of nano-particles, causing an increased softening degree. Trace TiC/TiB 2 nano-particles exhibit good plasticizing effect. [ABSTRACT FROM AUTHOR]