Effects of AlN on the densification and mechanical properties of pressureless-sintered SiC ceramics

In the present work, Si C ceramics was fabricated with Al N using B_4 C and C as sintering aids by a solid-state pressureless-sintered method. The effects of Al N contents on the densification, mechanical properties, phase compositions, and microstructure evolutions of as-obtained Si C ceramics were thoroughly investigated. Al N was found to promote further densification of the Si C ceramics due to its evaporation over 1800 °C,transportation, and solidification in the pores resulted from Si C grain coarsening. The highest relative density of 99.65% was achieved for Si C sample with 15.0 wt% Al N by the pressureless-sintered method at 2130 °C for 1 h in Ar atmosphere. Furthermore, the fracture mechanism for Si C ceramics containing Al N tended to transfer from single transgranular fracture mode to both transgranular fracture and intergranular fracture modes when the sample with 30.0 wt% Al N sintered at 1900 °C for 1 h in Ar. Also, Si C ceramics with 30.0 wt% Al N exhibited the highest fracture toughness of 5.23 MPa m~(1/2) when sintered at 1900 °C.     

Sintering behaviour of feldspar and influence of electric charge effects

The characterization of feldspar for electric porcelain and the behaviour of these materials after heating at 1230℃ were studied. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were used to identify the present phases and the densification level. Feldspar sand was treated by flotation. The floated feldspar is constituted by microcline, quartz, and minor amounts of albite. The microstructure of sintered feldspar at 1230℃ is essentially vitreous with open microporosities. The dielectrical properties of composites were characterized by using the induced courant method (ICM), which indicates that the charge trapping capacity depends on the mineralogical and chemical composition of feldspar.     

Densification behavior of mechanically milled Cu–8 at% Cr alloy and its mechanical and electrical properties

Synthesis and consolidation behavior of Cu–8 at%Cr alloy powders made by mechanical alloying with elemental Cu and Cr powders,and subsequently,compressive and electrical properties of the consolidated alloys were studied.Solid solubility of Cr in Cu during milling,and subsequent phase transformations during sintering and heat treatment of sintered components were analyzed using X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The milled powders were compacted applying three different pressures(200 MPa,400 MPa and 600 MPa)and sintered in H2atmosphere at 900 1C for 30 min and at 1000 1C for 1 h and 2 h.The maximum densification(92.8%)was achieved for the sample compacted at 600 MPa and sintered for 1000 1C for 2 h.Hardness and densification behavior further increased for the compacts sintered at 900 1C for 30 min after rolling and annealing process.TEM investigation of the sintered compacts revealed the bimodal distribution of Cu grains with nano-sized Cr and Cr2O3precipitation along the grain boundary as well as in grain interior.Pinning of grain boundaries by the precipitates stabilized the fine grain structure in bimodal distribution.     

超细晶粒WC—Co硬质合金的收缩与晶粒长大

采用复合烧结工艺（真空烧结＋热等静压烧结）制备超细晶粒ＷＣ－Ｃｏ硬质合金，研究了烧结过程中的超细合金的收缩及晶粒长大行为。结果表明，在常规的固相烧结阶段，局部微区内的液相烧结使超细晶粒ＷＣ－Ｃｏ硬质合金的收缩及晶粒长大行为不同于普通晶粒硬质合金。在此阶段，ＷＣ晶粒出现较严重的早期晶粒长大现象，导致合金的收缩占总体收缩量的９０％以上。     

NdFeB系永磁体的矫顽力

根据TEM观察,建立了三元烧结NdFeB系永磁体的显微结构模型。运用微磁学理论对矫顽力模型作了计算,并讨论了Nd_2Fe_(14)B晶粒和NdFeB系永磁体的矫顽力。提出了烧结NdFeB系永磁体Nd_2Fe_(14)B晶粒的外延壳磁硬化理论和提高其矫顽力的途径。     

TiC/316L复合材料的致密化和力学性能试验

采用真空烧结法制备出TiC颗粒增强316L不锈钢复合材料.通过对试样进行光学显微分析并测定其相对密度和拉伸性能,研究了增强相含量和模压压力对复合材料的致密化和拉力学性能的影响,并对断口形貌进行分析.结果表明:添加TiC颗粒有利于复合材料的烧结致密化;TiC颗粒的体积分数对复合材料的拉力学性能有较大影响,当TiC的体积分数从0%增加到10%时,复合材料的抗拉强度从543MPa提高到655MPa,而断裂应变却从0.325减至0.052;在较低的模压压力下,提高模压压力有利于复合材料的相对密度、抗拉强度的增加;但过高的模压压力会使试样在烧结后残余封闭孔隙,降低复合材料的塑性性能和抗拉强度.当模压压力为500MPa时,可得到相对密度高、组织致密、增强相颗粒分布均匀、拉伸性能良好的复合材料.     

α-Al2O3纳米粉体的烧结行为

为了探讨在无压烧结过程中α-Al2O3纳米粉体的烧结行为和致密化过程,采用高分子网络凝胶法制备了α-Al2O3纳米粉体,经冷压成型后无压烧结了Al2O3陶瓷,结果表明:α-Al2O3晶种的加入明显降低了高分子网络凝胶法制备α-Al2O3粉体的相转变温度,在950℃较低温下就可获得α-Al2O3纳米粉体;生坯的相对密度随...     

Investigation of compaction and sintering behavior of SiC powder after ultra-fine treatment

Silicon carbide ceramics were prepared with SiC powder treated by the fluidized bed opposed jet mill as raw materials, and the effects of the ultra-fine treatment mechanism on the compaction and sintering behavior of SiC ceramics were investigated. The results showed that the compacts had higher density and microstructure homogeneity when the sintering temperature of the compact was decreased; and that the surface microstructure, densification and mechanical properties of the sintered body could be ameliorated obviously.     

SPCC钢与NdFeB永磁体的激光点焊

在电子、汽车及音响器件的制造中,稀土永磁材料NdFeB与钢构件之间连接通常采用机械连接或粘接的方法,而关于钢与磁材料焊接的研究与应用还未见报道.为实现钢磁异质材料之间快速和高质量的连接,该文探索采用激光点焊方法连接SPCC钢与NdFeB永磁体,并对接头的形成过程、硬度、强度和断裂行为进行了研究.结果表明:激光点焊过程中,两种母材受热快速熔化、混合、凝固形成接头;接头中硬度分布不均匀,热影响区的硬度比NdFeB母材低,熔核内熔核线附近区域硬度最高,熔核中部硬度最低;接头断裂应力可达到磁体强度的75%;熔核与磁体界面上容易出现热裂纹,结合较弱,因此剪切试验中接头主要从这一区域发生断裂,断裂为晶间断裂,是典型的脆性断裂.     

非稀土金属及合金化合物改性烧结NdFeB磁体的研究进展

研究发现,烧结钕铁硼(NdFeB)磁体的矫顽力(H_C)、腐蚀性与晶界相成分、微观结构息息相关.传统熔炼添加重稀土元素虽可改善晶界相提高磁体的H_C及抗蚀性,但同时也使添加物均匀地分布于主相,引起稀磁效应并使成本增加.通过晶界添加非稀土物质调控磁体晶界相,可优化晶界相微观结构,提高其电极电位及润湿性,从而在磁体H_C和耐蚀性得以改善的同时,降低磁体中重稀土元素的用量及成本.对近些年晶界添加非稀土金属及合金化合物调控烧结NdFeB晶界相成分、微观结构及其对磁体H_C、抗蚀性影响的部分研究进行了归纳.     

还原扩散法制备NdFeB磁体工艺研究

本文研究了用还原扩散法制备钕铁硼磁体的工艺,讨论了原料中钕含量,添加元素钴,铝的含量及洗涤液对磁性能的影响。     

Magnetic properties and thermal stability of sintered Nd-Fe-B magnet with Dy-Ni additive

A sintered(Nd_(0.8)Pr_(0.2))_(30.7)FebalB_(0.98)Cu_(0.2) magnet with 3% intergranular Dy_(85)Ni_(15) additive is prepared to study the magnetic properties and thermal stability of the Nd-Fe-B magnet. The results show that the magnet with or without additive obtains its optimum comprehensive magnetic properties at the sintering temperature of 1 030 ℃ and 1 040 ℃, respectively. The maximum coercivity of the magnet with additive reaches 15.16 k Oe, while that of the magnet without additive is just 11.88 k Oe. Further investigation on microstructure indicates that the grains of the magnet with additive form a modified "core shell" structure. Adding Dy_(85)Ni_(15) can significantly enhance the coercivity of Nd-Fe-B magnet and thus decrease its coercivity temperature coefficient.     

Spark plasma and microwave sintering of Al6061 and Al2124 alloys

Despite the importance of aluminum alloys as candidate materials for applications in aerospace and automotive industries, very little work has been published on spark plasma and microwave processing of aluminum alloys. In the present work, the possibility was explored to process Al2124 and Al6061 alloys by spark plasma and microwave sintering techniques, and the microstructures and properties were compared. The alloys were sintered for 20 min at 400, 450, and 500℃. It is found that compared to microwave sintering, spark plasma sintering is an effective way to obtain homogenous, dense, and hard alloys. Fully dense (100%) Al6061 and Al2124 alloys were obtained by spark plasma sintering for 20 min at 450 and 500℃, respectively. Maximum relative densities were achieved for Al6061 (92.52%) and Al2124 (93.52%) alloys by microwave sintering at 500℃ for 20 min. The Vickers microhardness of spark plasma sintered samples increases with the increase of sintering temperature from 400 to 500℃, and reaches the values of Hv 70.16 and Hv 117.10 for Al6061 and Al2124 alloys, respectively. For microwave sintered samples, the microhardness increases with the increase of sintering temperature from 400 to 450℃, and then decreases with the further increase of sintering temperature to 500℃.     

TiH2粉末制备钛合金的烧结脱氢规律及工艺

 以TiH₂粉末为原料,通过压制成型和烧结工艺制备粉末钛合金,不同于传统钛粉末冶金方法。通过热分析和热膨胀技术研究不同球磨粒度TiH₂粉末的脱氢和收缩规律,以此入手研究了TiH₂粉末压坯和TiH₂-Al-V粉末压坯的烧结致密特性,以及影响烧结过程的主要工艺因素,包括烧结温度、烧结时间、升温速率、压坯密度、压坯成型方式、合金体系,并对烧结组织进行了分析。结果表明,TiH₂粉末球磨后脱氢温度降低,粉末越细,开始温度越低。TiH₂粉末压坯在烧结过程中脱氢后获得新鲜钛,其易发生黏接并引起α-Ti的强烈收缩,这时烧结体很容易致密,并获得相对密度大于99%坯体;相比之下,TiH₂-Al-V粉末压坯烧结时因为合金元素的溶解,不如纯TiH₂粉末压坯的烧结容易致密。TiH₂-Al-V粉末经过成型、烧结脱氢可获得典型的层片状α+β钛合金组织,合金元素分布均匀。     

Nd-Fe-B磁体热等静压烧结的实验研究

研究了热等静压烧结对Nd-Fe-B磁体的致密度、显微组织及磁性能的影响.结果表明:与常压烧结磁体相比,热等静压烧结磁体的内部存在较多的孔洞,致密度、晶粒取向度及磁性都有所降低.用加热Ar气热膨胀而产生热等静压进行烧结的办法不适于制造高性能的烧结磁体.     

烧结工艺对透明氧化铝陶瓷性能的影响

以Isobam600AF为分散剂,Isobam104为胶黏剂,采用注凝成型工艺和真空无压烧结技术,通过改进两步烧结法制备了透明氧化铝陶瓷,探究了不同烧结温度和保温时间对氧化铝陶瓷晶粒尺寸、致密度、光学性能和力学性能的影响.结果表明:该烧结工艺可有效控制晶粒尺寸长大和提高相对密度,进而提高其光学性能和力学性能.在烧结过程中,当温度升高到一定范围时,致密化过程开始,且致密化速率随着温度的升高和保温时间的延长先增加后降低,在两步烧结1 400 ℃保温3 h时致密化速率达到最快.因此,坯体的致密化过程是非线性的,且具有一个最高致密化速率温度和保温时间点.     

Microwave sintering effects on the microstructure and mechanical properties of Ti-51at%Ni shape memory alloys

Ti-51at%Ni shape memory alloys (SMAs) were successfully produced via a powder metallurgy and microwave sintering technique. The influence of sintering parameters on porosity reduction, microstructure, phase transformation temperatures, and mechanical properties were investigated by optical microscopy, field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), compression tests, and microhardness tests. Varying the microwave temperature and holding time was found to strongly affect the density of porosity, presence of precipitates, transformation temperatures, and mechanical properties. The lowest density and smallest pore size were observed in the Ti-51at%Ni samples sintered at 900℃ for 5 min or at 900℃ for 30 min. The predominant martensite phases of β2 and β19' were observed in the microstructure of Ti-51at%Ni, and their existence varied in accordance with the sintering temperature and the holding time. In the DSC thermograms, multi-transformation peaks were observed during heating, whereas a single peak was observed during cooling; these peaks correspond to the presence of the β2, R, and β19' phases. The maximum strength and strain among the Ti-51at%Ni SMAs were 1376 MPa and 29%, respectively, for the sample sintered at 900℃ for 30 min because of this sample's minimal porosity.     

Facile synthesis of Ca-α-SiAlON:Eu2+ phosphor by the microwave sintering method and its photoluminescence properties

Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by conventional gas-pressure sintering technique at 1750℃.When it was excited at 450 nm,the as-prepared yellow Ca-SiAlON:Eu2+ sample had an external quantum efficiency of 42%,comparable to the sample synthesized at 1750℃ under 0.5 MPaN2 gas pressure by the GPS method reported in reference.The experimental results demonstrated that the microwave sintering method was also an interesting approach for synthesizing nitride phosphors,which promises lower firing temperature than those by carbothermal reduction and nitridation (CRN) methods,higher heating rate and shorter duration time compared with those by gas-pressure sintering.     

Effect of sintering temperature on phase evolution of Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) bulk amorphous composites synthesized via mechanical alloying and spark plasma sintering

Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) amorphous powders were synthesized by mechanical alloying for 200 h. Subsequent consolidation was performed via spark plasma sintering in the temperature range of 250 ℃ to 500 ℃ at the pressure of 500 MPa. The role of viscous flow on densification was investigated by studying the viscosity change of the amorphous phase at different consolidation temperatures. The decrease in viscosity at higher sintering temperatures resulted in better particle bonding and densification of consolidated samples. The formation of only FCC Al was observed in the consolidated samples at sintering temperatures ≤ 300 ℃ and the intermetallic phases formed at temperatures ≥ 400 ℃. The mechanical properties of the bulk samples were measured by Vickers microhardness and nanoindentation tests. The testing results showed that the average values of microhardness, nanohardness and elastic modulus of the sample consolidated at 500 ℃ were 3.06 ± 0.14 GPa,4.85 ± 1.14 GPa and 89.53 ± 9.25 GPa, respectively. The increase in hardness and elastic modulus of the higher temperature consolidated samples is attributed to the improvement in particle bonding, densification and distribution of various hard intermetallic phases in the amorphous matrix.     

烧结NdFeB磁体表面化学镀Ni-Cu-P合金及防腐性能

在烧结NdFeB磁体表面化学镀Ni-Cu-P以提高其耐腐蚀性能. 研究了络合剂的质量浓度、镀液的pH值、施镀温度及金属离子配比[Cu2 ]/[Ni2 ]对沉积速度和镀层成分的影响. 用扫描电镜(SEM)和能谱仪(EDAX)观察镀层形貌并分析镀层成分. 测定Ni-Cu-P合金镀层在质量分数3.5% NaCl溶液中的极化曲线,并结合中性盐雾实验表征镀层的耐腐蚀性能. 研究表明:烧结NdFeB永磁体经碱性超声波除油、酸洗活化后进行化学镀Ni-Cu-P,可得到结合力良好的合金镀层;随着镀液中金属离子配比[Cu2 ]/[Ni2 ]的增大,所得镀层从非晶向晶态转变,镀层中的磷含量先升高后降低,镀层表面变得平整、致密;化学镀Ni-Cu-P三元合金的耐腐蚀性能优于相同条件下所得到的Ni-P镀层,且从金属离子配比([Cu2 ]/[Ni2 ])为0.02的镀液中得到的镀层的耐腐蚀性能最强.