Microwave sintering of W-15Cu ultrafine composite powder prepared by spray drying &; calcining-continuous reduction technology

The effects of microwave sintering and conventional H2 sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying & calcining-continuous reduction technology were investigated.In comparison to the conventional H2 sintering processing,microwave sintering to W-15Cu can be achieved at lower sintering temperature and shorter sintering time.Furthermore,higher performances in microwave sintered compacts were obtained,but high microwave sintering temperature or long microwave sintering time could result in coarser microstructures.     

Microstructure and properties of W-15Cu alloys prepared by mechanical alloying and spark plasma sintering process

W-15Cu composite powders prepared by mechanical alloying （MA） of raw powders were consolidated by spark plasma sintering （SPS） process at temperature ranged 1 230-1 300 ℃ for 10 min and under a pressure of 30 MPa. By using high energy milling, particles containing very fine tungsten grains embedded in copper, called composite particles, could be produced. The W grains were homogeneously dispersed in copper phase, which was very important to obtain W-Cu alloy with high mechanical properties, fine and homogeneous microstructure. The microstructure and properties of W-15Cu alloys prepared by SPS processes at different temperature were researched. The results show that W-15Cu alloys consolidated by SPS can reach 99.6 % relative density, and transverse rupture strength （TRS） is 1 400.9 MPa, Rockwell C hardness （HRC） is 45.2, the thermal conductivity is 196 W/m-K at room temperature, the average grain size is less than 2 μm, and W-15Cu alloy with excellent properties, homogeneous and fine microstructure is obtained.     

Properties, phases and microstructure of microwave sintered W-20Cu composites from spray pyrolysiscontinuous reduction processed powders

The effects of microwave sintering on the properties, phases and microstructure of W-20Cu alloy, using composite powder fabricated by spray pyrolysis-continuous reduction technology, were investigated. Compared with the conventional hot-press sintering, microwave sintering to W-20Cu composites could be achieved with lower sintering temperature and shorter sintering time. Furthermore, microwave sintered W-Cu composites with high densification, homogenous microstructure and excellent properties were obtained. Microwave sintering could also result in finer microstructures.     

Effects of cryogenic treatment on mechanical properties and microstructure of Fe-Cr-Mo-Ni-C-Co alloy

Fe-Cr-Mo-Ni-C-Co alloy was quenched in liquid nitrogen and held for 24 h. Hardness tester, OM, XRD, SEM were used to investigate the mechanical properties and microstructures of the alloy. The results show that the hardness increases by 1-2 （HRC） and the compressive strength decreases slightly after cryogenic treatment. The increase in hardness is attributed to the transformation from austenite to martensite and the precipitation of the very tiny carbide η-Fe2C. The decrease in compressive strength is caused by residual stress. The great amount of carbides, such as Cr7C3 and Fe2MoC, in the alloy and the obvious difference in thermal expansion coefficient between these carbides and the matrix at the cryogenic temperatures lead to this residual stress. The microscopy of cryogenic martensite is different from that of the non-cryogenic martensite. The cryogenic martensite is long and fine; while the non-cryogenic martensite is short and coarse. There is obvious surface relief of the cryogenic martensite transformation. It is not orientational of this kind surface relief and the boundary of this surface relief is smooth and in a shape of butterfly. The surface relief in the non-cryogenic martensite is wide and arranged in parallel, and the boundary of surface relief is not smooth. These characteristics may imply different growth ways of the two kinds of martensite.     

抑制剂对W-15Cu合金性能与结构影响研究

以喷雾干燥-共还原法制备的W-15Cu超细复合粉末为原料,采用氢气活化烧结制备了W-15Cu高比重合金,研究了晶粒生长抑制剂Y2O3对合金性能与结构的影响。利用扫描电镜、维氏硬度仪、密度测试仪、金相显微镜等,观察烧结体显微结构,测试其硬度、密度与断裂强度。结果表明,在最佳烧结温度下,添加质量分数0.3%Y2O3的W-15Cu合金抗弯强度达到最大值1 128.6 MPa,添加质量分数0.5%Y2O3的W-15Cu维氏硬度达到最大值2.78 GPa,优于未添加抑制剂的W-15Cu合金。Y2O3可以细化W晶粒。     

Kinetic characteristics of liquid phase sintering of mechanically activated W-15wt% Cu powder

The kinetic characteristics of W grain growth operated by diffusion controlled Oswald ripening （DOR） during liquid phase sintering were studied. A liquid phase sintering of W-15wt%Cu was carried out by pushing compacts into a furnace at the moment when the temperature increased to 1340℃ for different sintering times. The results show that liquid phase sintering produces the compacts with considerably low relative density and inversely, rather high homogeneity. On the basis of the data extracted from the SEM images, the kinetic equation of W grain growth, G^n = G0^n ＋ kt, is determined in which the grain growth exponent n is 3 and the grain growth rate constant k is 0.15 μm^3/s. The cumulative normalized grain size distributions produced by different sintering times show self-similar. The cumulative distribution function is extracted from the curves by non-linear fitting. In addition, the sintering kinetic characteristics of W-15wt%Cu compacts were also investigated.     

钕对AZ91镁合金组织及机械性能的影响

采用微观分析、机械性能测试及断口分析等方法研究了钕对AZ91-Nd镁合金(w(Nd)=0,0.1%,0.3%,0.5%,1.0%,1.5%)的微观组织和机械性能的影响。结果表明:Nd以固溶和金属间化合物(A l11Nd3)的形式存在时具有细化晶粒、抑制二次β相析出、使不完全离异共晶转化为离异共晶的作用;Nd通过固溶强化、析出强化和细晶强化增加了合金强度和硬度,并改善了塑性;加入Nd后合金的断裂机制从脆性解理断裂转变为准解理断裂。     

Effects of Ag on microstructure and mechanical properties of 2519 aluminum alloy

The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3 % （mass fraction） Ag accelerates 2519 aluminum alloy＇s age-hardening, increases its peak hardness and reduces 4 h of peak aged time at 180 ℃. The addition of 0. 3% （mass fraction） Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200 ℃ is 24 MPa and 78 MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.     

Effect of sintering atmosphere on microstructure and properties of TiC based cermets

The effect of the sintering atmospheres （vacuum, N2, Ar） on the microstructures and properties of the TiC based cermets was studied using XRD, SEM/BSE and energy dispersive spectrometer. Compared with the alloy sintered in vacuum, the carbon content of the specimen sintered in N2 and Ar is lower by 0.5%; and the nitrogen content is higher by 0.3% when sintered in nitrogen. The central part of the ring structure may be carbide with either a high W or Ti content. The ring structures are （Ti, W, Ta, Mo, Co, Ni）C solid solutions with different metallic elements and distributions. The composition of the binder phase is （Co, Ni） solid solution with different Ti, W, Ta, Mo, C contents. The structures are uniform for the cermets sintered in vacuum and the properties are the best. When sintered in Ar or N2, the O2 and N2 in the atmosphere take part in the sintering reaction to break the carbon balance in the cermets to form a shell structure and defects, which results in poor density, microhardness （HV） and transverse rupture strength （TRS）.     

TiB2/Cu复合材料组织与性能的研究

以Ti、B和Cu的单质粉末为原料,经混粉-冷压成形-真空烧结,制备出原位自生TiB2陶瓷颗粒增强铜基复合材料.并借助热分析方法和X射线衍射对增强颗粒进行分析,同时通过扫描电子显微镜对复合材料组织进行观察,进一步测定复合材料的力学性能.结果表明,在Ti-B-Cu体系中,通过原位反应生成增强相是TiB2.随着B粉和Ti粉含...     

Effects of cerium on microstructure and mechanical properties of ZK60 alloy

ZK60-xcerium alloys were studied,where x mass fraction is 0, 0.52%, 0.94%, 1.51% and 1.98%, respectively. Influence of Ce contents and heat-treatment on microstructure and tensile properties was analyzed. The results show that cast ZK60 alloy containing no Ce has coarse crystal grains, and lots of segregation aggregates around the grain-boundary. However, the alloys containing Ce have refined grains, and grain-boundaries are purified at the same time. Obvious dynamic recrystallization occurs in tested alloys after hot-extrusion. Tensile strength heightens with the increase of Ce content, and grows higher after aging at 150℃ for 0 -24 h （T5 treatment）. Comparing tensile properties of investigated alloys in different states, it can be concluded that synthetical properties of the alloy with 1.51% Ce addition is the best of all. In extruded state, σb and δ of this alloy are 318.6 MPa and 14.4%, respectively. After aging for 24 h ,σb is 338.6 MPa and δ is 15.6%.     

Sintering behavior, microstructure and properties of TiC-FeCr hard alloy

TiC based cermets were produced with FeCr, as a binder, by conventional P/M （powder metallurgy） to near 〉97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of 〉1360℃ caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360℃ for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettabifity of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals.     

Effects of sintering temperature on microstructure and performance of Ti-based Ti-Mn alloy anodic material

A novel Ti-based Ti-Mn composite anode used for electrolytic manganese dioxide(EMD) fabrication was developed by a two-step heating manganizing technique.The effects of sintering temperature on the manganized microstructure and the performance of the composite anode were studied by scanning electron microscopy(SEM),mechanical properties tests at room temperature and electrochemical methods.The results show that the thickness of the diffusion layer increases with the increase of sintering temperature up to 1...     

Effect of heat treatments on tensile properties and microstructure of 2195 alloy

Effect of various aging treatments on the tensile properties and microstructure of 2195 alloy has been investigated. The experimental results show that promising combination of strength and ductility is achievable under T₈ temper. The lower aging temperature reduces T₁ precipitation on the subgrain or grain boundaries and favors uniform dispersion of T₁ phases in the matrix, resulting in better strength and ductility. Prior deformation before aging has improved tensile strength with a slight decrease in ductility. Pre-aging after prior deformation had little effect on the age-hardening behavior of 2195 alloy. Project supported by the Key Program of the 9th Five-year Plan of China Synopsis of the first author Zheng Ziqiao, professor, born in 1944, major research fields: physical metallurgy of aluminum alloys; functionally gradient materials; self-propagation high temperature synthesis.     

Effects of annealing on microstructure, mechanical and electrical properties of AlCrCuFeMnTi high entropy alloy

The multi-component A1CrCuFeMnTi high entropy alloy was prepared using a vacuum arc melting process. Serial annealing processes were subsequently performed at 590 ℃, 750 ℃, 955 ℃ and 1 100 ℃ respectively with a holding time of 4 h at each temperature. The effects of annealing on microstructure, mechanical and electrical properties of as-cast alloy were investigated by using differential thermal analysis （DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that two C14 hexagonal structures remain unchanged after annealing the as-cast A1CrCuFeMnTi alloy specimens being heated to 1 100℃. Both annealed and as-cast microstructures show typical cast-dendrite morphology and similar elemental segregation. The hardness of alloys declines as the annealing temperature increases while the strength of as-cast alloy improves obviously by the annealing treatment. The electrical conductivities of annealed and as-cast alloys are influenced by the distribution of interdendrite re~ions which is rich in Cu element.     

Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties, electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated. The results indicated that with elevating the aging temperature from 100℃ to 160℃, the aging response rate was greatly accelerated, and the UTS at peak aging condition decreased, while the corresponding TYS increased. However, the electrical conductivity of the alloy became higher. After aging for 24 h at 120℃, the peak UTS and TYS values were achieved as 591 MPa and 541 MPa, respectively; but the alloy achieved a lower conductivity, 20.4 MS/m. When T6 temper was performed at 140℃ for 14 h, the UTS decreased only by 1% of the former, whereas the TYS and the electrical conductivity increased obviously, which were up to 559 MPa and 22.6 MS/m, respectively. The major strengthening precipitates of the peak-aged alloy were GP zones and η′ phase. The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature. There were obvious PFZs along the grain boundary both in T6 conditions aged at 140℃ and 160℃.     

Effects of heat treatment on the microstructure and mechanical properties of ZA84 magnesium alloy

The effects of heat treatment on the microstructure and mechanical properties of ZA84 (Mg-8Zn-4Al-0.25Mn) alloy were investigated. The results indicate that the as-cast microstructure of the alloy is mainly composed of α-Mg matrix and two different morphologies of precipitates (continuous and quasi-continuous Mg32(Al,Zn)49 phases and isolated Mg5Al2Zn2 phases). After solid solution treatment at 345°C, the Mg32(Al,Zn)49 phases change from continuous and quasi-continuous net to disconnected acute angle shape,...     

热处理对反向挤压AZ80镁合金组织与性能的影响

采用光学和扫描电子显微观察、X射线衍射及拉伸试验研究了反向挤压AZ80镁合金不同热处理状态下的显微组织及性能．结果表明：反向挤压AZ80镁合金热处理后析出的β－Mg17Al12相（β相）在不同热处理状态下形貌不同．经T6热处理后,口相在晶界处呈层片状析出,与挤压态相比,合金的强度稍有降低,但延伸率明显提高;经T5热处理后,卢相在晶界处仍呈层片状,而在晶内呈颗粒状,与挤压态相比,合金的强度明显提高,但延伸率降低．     

Effects of sintering atmosphere on the microstructure and mechanical property of sintered 316L stainless steel

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Effects of heat treatment on microstructure and mechanical properties of Fe-Co-Ni-Cr-Mo-C alloy

A kind of Fe-Co-Ni-Cr-Mo-C alloy was designed for valve seat use. The effects of the quenching temperature, tempering time and tempering temperature on the mechanical properties and microstructure of the alloy were investigated. The results show that the hardness decreases, while tensile strength (σb), transverse rupture strength (σbb) and impact toughness(Kit) increase after the alloy is quenched and tempered. The best complex property (σb, 446 MPa; σbb ,793 MPa; Kic, 2.96 J/cm2 ) can be obtained when the alloy is quenched at 1 100 ℃ and tempered at 650 ℃. The results of X-ray diffraction and energy dispersive X-ray analysis (EDX) show that the major strengthening phases are carbides such as (Fe, Cr)7 C3 and Fe2 MoC. The obvious secondary hardening appears when the alloy is tempered at 550 ℃, which results from the precipitated carbides of Cr and Mo in the alloy from the matrix and the heat-resistant retained austenite .