Effect of La_2O_3 on microstructure and high-temperature wear property of hot-press sintering FeAl intermetallic compound

FeAl intermetallic compound with different contents of rare earth oxide La2O3 addition was prepared by hot pressing the mechanically alloyed powders.Effect of La2O3 on microstructure and high-temperature wear property of the sintered FeAl samples was investigated in this paper.The results showed that 1 wt.% La2O3 addition could refine the microstructure and increase the density of the FeAl intermetallic compound,and correspondingly improved the high-temperature wear resistance.SEM and EDS analyses of the wo...

Synthesis and Tribological Behaviors of Ti_3SiC_2 Material Prepared by Vacuum Sintering Technique

The bulk Ti3SiC2 specimens with less than 1 wt% TiC impurity were prepared by vacuum sintering technique, and the average grain size was about 5-6 μm in the elongated direction. When the sintering temperature, soaking time and heating rate were 1 400 ℃, 1 h and 10℃·min-1, respectively, the highest relative density of Ti3SiC2 specimens could reach 97.8%. Meanwhile, the lowest coefficient of friction （COF） and wear rate （WR） of the Ti3SiC2 samples were 0.55 and 1.37×10-3 mm3（Nm）-1 at a sliding speed of 0.35 m/s, load pressure of 10 N and ambient condition, respectively. The COF of the Ti3SiC2 sample reduced with the increasing of the load pressure, while the WRs fluctuated little. The WR increased with the increasing of the sliding speed, and weakly influenced the COF. These changing behaviors could be attributed to the presence and coverage of the amorphous mixture oxide film ofTi, Si, A1, and Fe on the Ti3SiC2 friction surface. The self- antifriction mechanism led to reducing of the COF. The increasing of the WR was attributed to the wearing consumption.

Preparation of Fe-As alloys by mechanical alloying and vacuum hot-pressed sintering:microstructure evolution,mechanical properties,and mechanisms

Arsenic materials have attracted great attention due to their unique properties.However,research concerning iron-arsenic(Fe-As) alloys is very scarce due to the volatility of As at low temperature and the high melting point of Fe.Herein,a new Fe-As alloy was obtained by mechanical alloying(MA) followed by vacuum hot-pressed sintering(VHPS).Moreover,a systematic study was carried out on the microstructural evolution,phase composition,leaching toxicity of As,and physical and mechanical properties of Fe-As alloys with varying weight fractions of As(20%,25%,30%,35%,45%,55%,65%,and 75%).The results showed that pre-alloyed metallic powders(PAMPs) have a fine grain size and specific supersaturated solid solution after MA,which could effectively improve the mechanical properties of Fe-As alloys by VHPS.A high density(> 7.350 g·cm^(-3)),low toxicity,and excellent mechanical properties could be obtained for FeAs alloys sintered via VHPS by adding an appropriate amount of As,which is more valuable than commercial Fe-As products.The Fe-25% As alloy with low toxicity and a relatively high density(7.635 g·cm^(-3)) provides an ultra-high compressive strength(1989.19 MPa),while the Fe-65% As alloy owns the maximum Vickers hardness(HVo.5 899.41).After leaching by the toxicity characteristic leaching procedure(TCLP),these alloys could still maintain good mechanical performance,and the strengthening mechanisms of Fe-As alloys before and after leaching were clarified.Changes in the grain size,micro structure,and phase distribution induced significant differences in the compressive strength and hardness.

Reactive Hot-press Sintering of Al-B_4C Composites at Relative Low Temperature

A new process of reactive hot-press sintering with boron carbide(B4C) and aluminum powders was proposed to overcome difficulties in the sintering of dense B4C ceramic materials.The B4C powder with different content of pure metallic aluminum particle were milled,hot-pressed and sintered at 1600 ℃ for 1 hour.The mechanism of sintering at relative low temperature was analyzed.The phase constitution of the composites was determined.Effects of Al content on the hardness and fracture toughness of the composites were discussed.The results show that thermite reaction procedure in B2O3+Al was the mechanism of sintering at relative low temperature,B4C,Al2O3 and metallic aluminum are the major constituents of the composites.The microhardness of the composites decreases with the increasing of Al content,but the fracture toughness increase obviously.The composite with 5wt% Al content has the best microhardness and fracture toughness in all the composites.

Distinct Electrical and Mechanical Responses of a Cu-10Fe Composite Prepared by Hot-Pressed Sintering and Post Treatment

A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behavior and performance changes were systematically studied by using scanning electron microscopy and transmission electron microscopy.In contrast to the hot-pressed sintered specimen,the solution treatment significantly affects the thermal stability and properties of the Cu-10wt%Fe composite.The Cu-10wt%Fe composite was prepared after solid solution,cold rolling and aging at 773 K for 1 h,and it obtained excellent tensile strength of 494 MPa,uniform elongation of 16.3%,electrical conductivity of 51.1%IACS and softening temperature of 838 K.Mechanisms for the distinct difference in thermal stability and properties between hot-pressed sintered and solution treated specimens were analyzed.These findings provide a theoretical basis for designing high-performance Cu-based in-situ composites by post treatment.

High-pressure Sintering of Boron Carbide-Titanium Diboride Composites and Its Densification Mechanism

A high-pressure hot-pressing process was applied to densify a commercial boron carbide-titanium diboride (B4C-TiB2) powder mixture.Nearly fully dense (98.6%) materials were obtained at 1700℃ under a pressure of 100MPa.Compared to the sintering temperature required to achieve similar results when a pressure of only 30MPa was applied,the sintering temperature was found to decrease by about 200℃ under pressure of 100 MPa.Analysis of the thermodynamics and microstructure showed that the plastic deformation of the B4C grains induced by high pressure dominated the densification mechanism when high pressure was applied.Furthermore,higher pressure resulted in remarkably improved mechanical properties of the composites,which could be traced back to the generation of stacking faults in the B4C grains and aggregation of TiB2.

Influence of Interfacial Diffusion on Mechanical Property of Vacuum Fusion Sinter (VFS) WC-Co Composite Coating

The WC-Co composite coatings bonded tightly to steel substrate have been made by vacuum fusion sinter （VFS）. The concentration distribution of some components were measured by the electron probe, and the microstructure and morphology of VFS coatings were observed and analyzed by SEM, X-ray diffractometer and microhardness tester. Diffusion coefficient of every element was calculated by using the experimental results. The influence of the interracial diffusion on the microstructure, Vickers hardness and interracial bond strength of the VFS coatings was studied in detail. The experimental results show that there is a metallurgical bond area between the VFS WC-Co coatings and the steel substrate. The VFS coatings are characterized by the gradient hardness of the interface and the high bond strength to the steel substate, both of which are beneficial to the improvement of the wear resistance and corrosion resistance.

Repetitious-Hot-Pressing Technique in Hot-Pressing Process

A new pressing method was proposed for hot-pressing process. Experimental results indicated that the porosity in Al2O3/TiC/ Ni/Mo (hereafter called AI2O3/TiC composite) composite compacts decreases by 6% after adopting this new technique, compared to traditional hot-pressing technique under the same sintering temperature. The flexural strength and Vicker hardness increase from 883 MPa to 980 MPa and from 16 GPa to 21.1 GPa, respectively. A theoretical model was given to analyze the densification mechanism of the composite in the process of repetitious-hot-pressing.

Manufacture of the Ultrafine Grain WC/Co Cemented Carbides by Combined Sintering Processing

A new kind of sintering process, combined sintering process. i.e. vacuum sintering plus hot isolate pressure sintering (HIP), was introduced for producing ultrafine WC-10% Co (mass fraction. so as the follows) cemented carbides. The effects of some processing parameters on the microstructure and mechanical properties of the obtained cemented carbides were studied. The results show that the rapid shrinkage and the pronounced densification of tile cemented carbides took place during the vacuum sintering stage, which is intinaately correlated with the local liquid sintering occurred during this earl} sintering stage for the high surface activity of ultrafine WC-Co powder. The way of high pressure imposing. isothermal treatment cycle during ac.acuum sintering and HIP sintering stage directly influence the densitication of compacts and the mechanical properties of the produced WC-10%Co cemented carbides.

High Temperature Sintering and Oxidation Behavior in Plasma Sprayed TBCs [Single Splat Studies] Paper 1—Role of Heat Treatment Variations

The TBC system is examined with regards to its response to thermal exposure at high temperature. It has been established before that the thermally grown oxide (TGO) layer that forms upon bond coat oxidation is the key factor determining the performance of the TBC system and/or its failure. However, characteristics of TGO growth, bond coat rumpling, principles governing failure of TBC systems and the various failure mechanisms have been studied extensively in case of just super alloy with bond coat or with thick top coating. In this study super alloy/bond coat system with single splats of YSZ instead of thick topcoat is analyzed in order to scrutinize the effect on the first layer of splats during thermal exposure. The splats with microcracks are the building blocks of the top coat. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. The interactions between the YSZ splats and the evolving TGO is directly linked to the presence or absence of bond coat oxidation. Therefore the high temperature behavior of this system is analyzed with variations in heat treatment involving, temperature, duration and environment of thermal exposure.

High Temperature Sintering and Oxidation Behavior in Plasma Sprayed TBCs [Single Splat Studies] Paper 2—Relevance of Variation in Materials Systems of TBC Components

The TBC system’s response to thermal exposure at high temperature is discussed here. The relevance of the microstructural aspects of each component of the TBC system is emphasized. The top coat is a YSZ ceramic coating consisting of a collection of splats on top of one another. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. This study investigates the effect of thermal exposure on the microstructure and sintering behavior in single splats produced using different starting powders since this has been shown to influence the basic microstructure of YSZ topcoat. The bond coat is an MCrAlY metallic coating which serves as an Al reservoir and allows the formation of a protective alumina, Thermally Grown Oxide (TGO) layer between the bond coat (BC) and the top coat (TC) layers. This oxide scale formed upon thermal exposure prevents further oxidation of the underlying component (substrate) and thus provides protection. As such, the content of free Al in the bond coat layer is of significance and makes it crucial to understand the influence of bond coat microstructure evolution and oxidation involved during its formation. The interaction between the bond coat, the TGO and the top coat layers is examined in this study to understand the high temperature behavior of the TBC system with regards to variations in the top coat and bond coat material systems used.

Preparation and Properties of Si2N2O Ceramics for Microwave Sintering Furnaces

Si2N2O ceramics were prepared using amorphous Si3N4 as the raw material and Li2CO3 as the sintering additive through vacuum multi-stage sintering.The influence of the Li2CO3 addition(0%,1%,2%,3%,and 5%,by mass)on the phase composition,the microstructure,the porosity,the mechanical properties,the dielectric constant and the tangent of the dielectric loss angle of the porous Si2N2O ceramics was investigated.The results reveal that a suitable addition of Li2CO3 can promote the generation of Si2N2O but excessive or inadequate Li2CO3 causes decomposition of Si2N2O ceramics.The prepared porous Si2N2O ceramics have good mechanical properties,good thermal shock resistance,and low dielectric properties,which have excellent potential for application in microwave sintering furnaces.

Mechanical Properties of a Vacuum-Sintered Apatite Body for Use as Artificial Bone

Regenerative artificial bone material and bone parts were fabricated using vacuum-sintered bodies of a “titanium medical apatite (TMA?)” that is formed by chemically connecting Ti oxide molecules to the reactive [Ca10 (PO4 )6 ] group of hydroxyapatite (HAp). Sintering at temperatures of 1273 - 1773 K caused this TMA sintered bodies to recrystallize and form a varying mix of α-TCP (tricalcium phosphate), β-TCP and Perovskite-CaTiO3 phases. The Perovskite crystals proved to be quite stable and hard, forming a uniform distribution of similarly sized fibers in all directions under vacuum sintering, but an irregular distribution and size when sintered in the presence of oxygen. Complete recrystallization was achieved by vacuum sintering at temperatures in excess of 1473 K. In particular, TMA vacuum-sintered bodies at 1573 K are given the maximum value;a Vickers hardness of 400, a bending strength of 43 MPa, a compressive strength of 270 MPa and a density of approximately 2300 kg/m3 was achieved that closely corresponds to that of compact bone or a tooth. As these TMA bodies could also be cut into various forms, they are considered a promising biomaterial for use as artificial bone in the regeneration of natural bone, or to provide reinforcement of bone junctions in dental and orthopedic surgery.

Sintering densification and properties of Al_2O_3/PSZ(3Y) ceramic composites

The content of partially stabilized zirconia has remarkable influence on densification and mechanical properties of Al2O3/PSZ（3Y） ceramic composites. When 15%PSZ（3Y） is added to Al2O3, after vacuum sintering for 2 h at 1 550 ℃, the fracture toughness and bending strength of the Al2O3/PSZ（3Y） ceramic composite reaches 8.2 MPa·m1/2 and 884 MPa, respectively. The effect of the content of PSZ（3Y） on relative density and mechanical properties was investigated. The change of m-ZrO2 and t-ZrO2 phases content before and after fracture was measured by X-ray diffraction quantitative phase analysis. It is confirmed that improvement in bending strength and fracture toughness of the Al2O3/PSZ（3Y） ceramic composite is due to the phase transformation toughening mechanism of PSZ（3Y）.

石墨膜/铝复合材料制备工艺与性能研究

将石墨膜和铝箔以铺层的形式交替排布,采用真空热压烧结技术制备石墨膜/铝复合材料,研究真空热压烧结参数对复合材料微观组织和性能的影响。结果表明:石墨膜在复合材料中分布均匀,符合预期构型设计;真空热压烧结参数对复合材料微观组织影响显著,优化后的制备工艺参数为640℃/50 MPa/100 min,该条件下制备的复合材料界面结合良好,致密度高,没有检测到Al_(4)C_(3)相;随着石墨膜体积分数的增加,复合材料面内热导率呈现先增加后下降的趋势,石墨膜体积分数为30%时,复合材料面内热导率最大,为219.71 W/(m·K)。

真空热压烧结铌酸锂压电陶瓷研究

采用真空热压烧结法对铌酸锂粉体进行烧结制备铌酸锂压电陶瓷,通过改变烧结温度、保温时间来确定最佳烧结方案;对烧结样品的密度、显微结构、物相组成、压电和介电等性能进行了测试。研究表明:在烧结温度900℃、保温时间120 min、压力35 MPa条件下制备的铌酸锂压电陶瓷致密度最高(4.62 g/cm^(3)),同时其压电常数d_(33)达最大(8.7 pC/N),相较于传统固相烧结法及CO_(2)激光烧结法,其压电常数分别提高7.9 pC/N和2.7 pC/N。当测试频率介于1 kHz~1 MHz时,不同制备条件下铌酸锂压电陶瓷的介电常数均呈现迅速下降后趋于稳定的趋势。

陶瓷基事故容错燃料的烧结技术研究进展

事故容错燃料(Accident Tolerant Fuel,ATF)自福岛核事件以来受到了广泛关注。以UO_(2)为代表的陶瓷基ATF因其高熔点、优异的抗辐照性能和化学稳定性等优势,是当前核燃料的研究主流。然而,陶瓷基ATF仍面临制备工艺复杂、成本较高等挑战。研究人员采用放电等离子烧结、闪烧等新型烧结技术制备陶瓷基ATF,在缩短烧结时间、降低烧结温度方面获得了进展。通过对UO_(2)基、UN基、U_(3)Si_(2)基、UC基等几种典型的ATF的烧结技术进行了分析归纳,探讨了不同烧结技术的特点和发展前景,并对未来开发ATF进行了展望。

Dy_(2)Zr_(2)O_(7)磁光透明陶瓷的制备及法拉第效应

以自制的Dy_(2)O_(3)超细粉与市售的ZrO_(2)粉料为主要原料,经球磨混合后通过高温固相反应合成了平均粒径约为150 nm的Dy_(2)Zr_(2)O_(7)粉体,再经过冷等静压成型和真空烧结获得了Dy_(2)Zr_(2)O_(7)磁光透明陶瓷。研究表明,该陶瓷样品具有典型的缺陷萤石结构,在635 nm波长处的直线透过率约为68%,达到了理论透过率的88%。Dy_(2)Zr_(2)O_(7)透明陶瓷在635,780,1 064 nm处的费尔德(Verdet)常数分别为(-182±7),(-118±2),(-48±1) rad·T^(-1)·m^(-1),在1 064 nm近红外波段处约为商用铽镓石榴石单晶的1.24倍,在635 nm可见光波段处约为铽镓石榴石单晶的1.33倍。研究结果证明Dy_(2)Zr_(2)O_(7)透明陶瓷是一种有潜力的新型磁光材料。

WC-TiC-VC-Fe硬质合金的显微组织及热震性能

采用真空烧结方法成功制备了WC-TiC-VC-Fe硬质合金,研究了TiC、VC添加对WC-Fe硬质合金的显微组织及热震性能的影响。结果表明:添加TiC、VC使硬质合金中形成了(W、Ti、V)C固溶体,随着TiC、VC含量的增加,WC的晶粒尺寸呈现先降低再升高趋势,WC晶粒尺寸最小为0.86μm;TiC和VC的添加量各为3 mass%时,硬质合金的性能最佳,热疲劳至材料失效的次数达160次。通过添加TiC、VC改变了硬质合金的热疲劳裂纹扩展方式,由于新生的相加大了WC之间的间距,有效地提升裂纹扩展阻力,使其抗热震性能提升。

亚微米球形Y_(2)O_(3)粉体及其透明陶瓷的制备

Y_(2)O_(3)以其优良的物理化学性质和在280 nm~8μm宽频段内的高透明性,而广泛应用于激光介质或光学窗口等领域。制备高透明的Y_(2)O_(3)陶瓷是目前的研究热点和难点,而高质量的粉体是制备高透明Y_(2)O_(3)陶瓷的关键,尿素均相沉淀法以其爆发成核和均匀可控的阴离子释放机制成为制备单分散颗粒的主要方法。本工作以硝酸钇和尿素为原料,采用尿素均相沉淀法制备了单分散、亚微米级的球形Y_(2)O_(3)粉体。采用不同方法研究了Y_(2)O_(3)前驱体和煅烧后粉体的结构、物相演变和形貌。前驱体的颗粒尺寸约为330 nm,800℃煅烧2 h得到的Y_(2)O_(3)粉体尺寸约为260 nm。在800℃煅烧后即可得到纯相的Y_(2)O_(3)粉体,粉体呈球形,分散性好,且粒径均匀。以该Y_(2)O_(3)粉体为原料,添加原子分数0.3%的Nb_(2)O_(5)为烧结助剂,在1780℃通过真空无压烧结成功制备了透明Y_(2)O_(3)陶瓷。材料的光学性质优良,即样品(厚度1 mm)的直线透过率在1100 nm处达到76.9%,在400 nm处达到65.6%。本工作为制备性能优良的Y_(2)O_(3)透明陶瓷提供了一种新的方法。