Influence of Shock Wave Treatment of Boron Carbide Powders on the Structure and Properties of Hot-Pressed Polycrystals Based on Such Powders

The influence of deformation pre-treatment (milling in a planetary mill and shock-wave treatment) of B₄C powders of different size composition on their structure as well as the structure and mechanical properties of samples that have been hot-pressed from these powders is investigated. It is shown that treatment by shock waves produces a substantial change in the structure of the powders, and this tends to increase the mechanical properties of the polycrystalline cakes. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 118–127, July–August, 2005.     

碳化硅晶须对C/C复合材料表面SiC涂层的影响

以三氯甲基硅烷(CH3SiCl3,MTS)为先驱体原料,采用化学气相沉积法(CVD)在C/C复合材料表面原位生长碳化硅晶须(SiCw)及制备SiC涂层,研究SiCw对SiC涂层微观形貌,织构及力学性能的影响。结果表明:SiCw不仅可促成SiC等轴颗粒的细化、生长完善,裂纹宽度减小、偏转明显,而且可使涂层的织构发生改变;同时,大量的空洞在SiCw处形成,使得内层SiC涂层硬度低于外层,从而导致整个SiC涂层的硬度和弹性模量降低。     

GdB6对热压烧结B4C材料性能的影响

对热压烧结法制备的B4C-GdB6材料进行了性能测试.结果表明在GdB6添加量为2%～8%的范围内,随其添加量的增加,B4C-GdB6材料的硬度增加,比单一B4C材料增加了78%;抗弯强度降低;断裂韧性先减小后增大,但变化不大.B4C-GdB6材料的断口扫描电镜分析发现,GdB6的加入改变了单一B4C材料的烧结状态,随添加量的增加,B4C晶粒显著增大,晶粒间排列致密,使孔隙逐渐消失.     

Preparation and Properties of Self-Reinforced Si_3N_4-Based Composites

ＰｒｅｐａｒａｔｉｏｎａｎｄＰｒｏｐｅｒｔｉｅｓｏｆＳｅｌｆ－ＲｅｉｎｆｏｒｃｅｄＳｉ＿３Ｎ＿４－ＢａｓｅｄＣｏｍｐｏｓｉｔｅｓＳＯＮＧＳｈｅｎＴａｉａｎｄＬＩＵＧｕａｎｇＺｕＰｒｅｐａｒａｔｉｏｎａｎｄＰｒｏｐｅｒｔｉｅｓｏｆＳｅｌｆ－Ｒｅｉｎｆｏ...     

Influence of the Composition and Structure of B4C - Al2O3 Ceramic on the Tribotechnical Characteristics in Friction Against Steel

The morphology and phase composition of friction surfaces and the tribotechnical properties of the (B₄C - Al₂O₃)-steel 45 system are studied under dry friction at various sliding velocities and contact loads. We have found that fine-grained secondary structures are formed on the friction surfaces. The morphology and phase composition of these structures depend on the ceramic composition and on the test conditions. A comprehensive investigation of friction surfaces, using x-ray, electron-diffraction electron-probe, and electron-microscopy analysis, has shown that the structure and morphology of the secondary phases determine the tribotechnical properties of ceramic-steel couples. The maximum wear resistance of B₄C ceramics containing 5-20 mass% Al₂O₃ is determined by the formation of dense secondary-phase thin films on the friction surface. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 49–59, May–June, 2005.     

碳化硼粒径对可燃毒物成形与烧结性能的影响

以碳化硼微粉和氢化锆-2粉为原料,用钢模成形方法在200～500MPa的压力下制备了碳化硼氢化锆坯体,坯体在高真空烧结炉中于1 100～1 300℃下烧结1h制得碳化硼锆合金可燃毒物中空芯块.用扫描电镜分析坯体的微观形貌,研究了成形压力与碳化硼含量对坯体和烧结体相对密度的影响.结果表明:碳化硼的粒径对粉料能否用钢模成形有关键性影响;碳化硼氢化锆坯体的相对密度随碳化硼含量的增加而略有降低,随成形压力的增加而明显增加;碳化硼微粉严重阻碍了碳化硼锆合金的烧结,即使碳化硼的含量仅为0.49％(质量分数),芯块的相对密度也会下降18％;提高烧结温度和增加成形压力对芯块的致密化有明显促进作用.     

热等静压法制备大尺寸铝基碳化硼复合材料及性能研究

采用热等静压法制备铝基碳化硼复合材料(Al-B4C)板材,测试板材的密度和抗拉强度,并观察复合材料的微观组织和拉伸断口形貌。结果表明,Al-31%B4C(质量分数)板材的尺寸为3 mm×200 mm×5000 mm;Al-31%B4C复合材料的相对密度大于99.69%,抗拉强度大于300 MPa,断后延伸率大于3%,B4C颗粒均匀分布在基体中,并与基体紧密结合;Al-B4C复合材料板材的力学性能符合工程用中子吸收材料的要求。比较含不同质量分数B4C颗粒(10%、15%、20%、25%、30%、31%、35%、40%)的Al-B4C复合材料性能,当B4C质量分数为10%~40%时,随基体中B4C颗粒含量的增加,Al-B4C复合材料的密度和相对密度均逐渐降低;当B4C质量分数为10%~35%时,随基体中B4C颗粒含量的增加,Al-B4C复合材料的抗拉强度逐渐增大,断后延伸率逐渐降低。     

Synthesis and physicomechanical properties of B4C-VB2 composites

We have studied the properties of composites in the B₄C-VB₂-C system, obtained by reaction synthesis with hot pressing. We have established that the presence of free carbon and vanadium boride in the ceramic makes it possible to activate the sintering process and to obtain a dense, highly dispersed ceramic with good structural homogeneity parameters for lower isothermal holding temperatures. The composite ceramic has higher hardness and bending strength over a broad range of vanadium boride content than the monophase ceramic based on boron carbide. The strength properties of the composite ceramic containing up to 8 vol.% vanadium boride are improved by means of a mechanism involving propagating cracks bending around obstacles. When the VB₂ concentration increases further, the properties of the composite are determined by a microcracking mechanism. In this case, we observe relatively small changes in the elastic characteristics, which depend linearly on the composition of the ceramic. Introducing vanadium boride into the material is also accompanied by an increase in the contact and microstructural strengths. The results obtained indicate that the new composite material is promising for fabricating wear-resistant and shock-resistant components of various structures and machines. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 59–72, January–February, 2006.     

多孔碳化硼的力学性能及其微观组织

采用无压烧结法制备得到了多孔的碳化硼,用扫描电镜研究了该材料的微观组织;并测定了不同孔隙率碳化硼的抗弯强度和密度,分析了多孔碳化硼的孔隙率与抗弯强度和密度的关系。研究结果表明:采用无压真空烧结法所制备的多孔碳化硼材料的微观组织烧结良好,烧结颈明显,孔隙大小比较均匀;当空隙率为30%时,所制备的多孔碳化硼密度为1.714 g/cm3,抗弯强度为100.85 MPa。     

Synthesis and properties of ceramics in the SiC — B4C — MeB2 system

The effect of impurities and additives of titanium and zirconium borides on the structure and mechanical properties of SiC — B₄C ceramics over a broad temperature range has been investigated. The ceramics was fabricated by hot pressing without a protective medium. Introduction of borides is accompanied by improvement in all the studied mechanical properties at room temperature, and the nature of hardening of the ceramics is practically independent of the type of SiC powders used. At high temperatures, the mechanical behavior of the ceramics is determined by the impurity composition: the ceramics obtained using abrasive powders loses strength beginning at 600°C, while using powders with decreased impurity content makes it possible to preserve the strength of the material up to a temperature of 1400°C. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 29–42, May–June, 2000.     

Effect of distribution of B4C on the mechanical behaviour of Al-6061/B4C composite

In this work, the effect of mixing parameters on the distribution of B₄C in 6061-Al alloy and its correlation with mechanical behaviour was studied. 6061-Al alloy powder was mixed with 10 mass-% B₄C powder in a ball mill and powder rotator mixer by varying mixing time from 1 to 5?h. Mixing was performed in both wet and dry conditions in a ball mill while only dry condition was used in the powder rotator mixer. The green compacts were sintered at 630°C. The quadrat method was used to quantify the distribution of B₄C particles in the microstructures of sintered Al/B₄C composite. The results showed that the distribution was improved with mixing time but the density, hardness and compression strength of Al/B₄C composites were reduced with time during ball milling. On the other hand, the distribution of reinforcement, density, hardness and compressive strength of Al/B₄C composites was improved with mixing time in the powder rotator mixer.     

Structure Formation of Multiphase Compacts in the System SiC′ ― Carbon. Part 3. Structure Formation in the System SiC′ ― Carbon during Sintering

The effect of particle size for the original silicon carbide and carbon powders and effects connected with influence of the original components structures, as well as the structure and phase composition of self-bonded silicon carbide are studied.     

zrc对等离子喷涂成形钼制品的影响

采用包覆法制备了Mo-ZrC复合粉末,采用等离子喷涂成形,再对其进行热等静压处理得到复合材料零部件.将其与纯钼粉末等离子喷涂成形零部件作对比.用阿基米德法测量两种零部件的相对密度；用显微硬度计测量它们的维氏硬度；用万能材料试验机测试它们的拉伸强度；用扫描电镜观察它们的截面和拉伸断口微观形貌.结果表明,加入的ZrC在基体中呈弥散分布,且分布均匀,填充了钼颗粒之间的部分空隙.纯钼材料拉伸断口呈沿晶断裂,而复合材料的拉伸断口出现了部分穿晶解理断裂.纯钼材料的相对密度为86.5％,拉伸强度及显微硬度都较低.而复合材料的相对密度为89.7％,力学性能有显著提高,拉伸强度提高到123 MPa,显微硬度提高到275 HV0.025.     

添加微量B元素对铸造TC4钛合金显微组织和力学性能的影响

为细化铸造TC4钛合金的晶粒,改善合金的力学性能,在合金中加入了少量B元素.结果表明:随着B含量逐步增加至0.06％(质量分数,下同),ZTC4钛合金晶粒尺寸从添加B之前的4.5mm细化至0.36mm,硼化物的主要分布也随之由晶粒内部分布转变为晶界处分布.当B含量为0.03％时,ZTC4钛材料具有最高的延伸率,但当B含量超过0.06％时,ZTC4钛材料拉伸时接近脆性断裂.导致ZTC4-0.06B材料几乎脆断的原因可能是B含量过多导致B化物分布由主要在晶粒内部转向晶界处.从晶粒细化效果和材料力学性能综合考量,铸造TC4钛合金中B的最佳添加量为0.02％～0.04％.     

Analysis of Microstructure and Mechanical Properties of Different Hot Stamped B‐bearing Steels

Hot stamping is a technique to produce ultra high strength automobile components. The common material used in hot stamping process is coated and/or uncoated 22MnB5 boron alloyed steel. Ferritic‐pearlitic microstructure in as‐delivered sheets is transformed to fully lath martensitic after hot stamping. In the present research, hot stamping under water or nitrogen cooling media was investigated using different boron alloyed steel grades. Microstructural analyses, linear and surface hardness profiling as well as tensile tests of hot stamped samples were performed. Various microstructures of fully bainitic and/or fully martensitic were produced. The resulting microstructures provided yield strengths of 650–1370 MPa and tensile strengths of 850–2000 MPa. There is an optimum carbon equivalent content for which the highest formability index value, UTS × A₂₅, is achieved. Using a nitrogen cooled punch resulted in higher yield strength without significant changes in ultimate tensile strength. It is concluded that a wide range of B‐bearing steels having an extended carbon equivalent range with an acceptable formability index value can be used by increasing the cooling rate in the die assembly.     

热压工艺对SiC陶瓷结构及性能的影响

以β-SiC为起始粉末，分别选择有、无液相出现的两种热压工艺制备碳化硅陶瓷，并研究了它们的微观结构和力学性能，探讨了热压工艺对SiC陶瓷结构及性能的影响。     

Composites with zirconium matrix reinforced with boron and silicon carbide fibers

Structural features of a composite material (CM) consisting of a plastic zirconium foil-like matrix reinforced with continuous high-strength fibers of boron or silicon carbide with a diameter of 100 μm (25 to 30 vol.%) are examined at testing temperatures up to 950 °C. Model specimens are compacted by diffusion welding in vacuum at 1100 °C. Structural studies reveal a diffusion interaction area at the fiber-matrix interface. Cracks and pores appear in the area at 1100 °C. The effect of the diffusion area thickness on CM mechanical properties is discussed. It is established that reinforcement of zirconium with B or SiC fibers provides 7 and 5 times higher strength at 950 °C, respectively. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 48–53, 2007.     

短纤维增强C-SiC复合材料的制备和性能

将T700或Nicalon-SiC短纤维、碳粉、硅粉和少量碳化硅粉混合,在1900℃热压烧结制备短纤维增强C-SiC复合材料,并对其组织、结构及性能进行了研究。结果表明:SiCf／C-SiC的相对密度和室温强度分别为95.3％和24.38MPa,均高于Cf／C-SiC的相对密度和室温强度,热压烧结过程中Cf的损伤严重。短纤雄增强C-SiC复合材料中,由于C相和SiC相的同时存在,在同一温度下的氧化行为表现为在氧化初期氧化质量损失率较大,C相的氧化起主要作用;随氧化时间的增长,氧化质量损失率逐渐减小;在氧化后期则质量增加,SiC相的惰性氧化起主要作用。SiCf／C-SiC复合材料的抗氧化性能优于Cf／C-SiC复合材料的抗氧化性能。SiCf／C-SiC复合材料在温度为1100℃～1400℃时,温度越高,氧化质量损失率越小,抗氧化性能越强。     

核反应堆用碳化硼芯块常压烧结工艺研究

以核级碳化硼粉为原料,酚醛树脂作粘结剂与助烧剂,用钢模成形方法制备出碳化硼生坯,在碳管炉中用常压烧结方法在2250℃保温40 min,制备出高温气冷堆控制棒用碳化硼环形芯块。用化学分析方法分析了原料粉与碳化硼烧结体的化学成分,用排水法对芯块的密度进行测试,研究了碳质量分数对碳化硼芯块密度的影响,用扫描电镜对生坯与芯块的微观结构进行研究,对1:1大尺寸碳化硼芯块的变形量进行统计。结果表明:碳对碳化硼具有很好的助烧作用,碳化硼的密度随碳含量的增加而增加,当碳质量分数为5%时,最高密度达到2.35 g/cm~3;碳掺量为3%时,制得的1:1碳化硼芯块的密度为2.0 g/cm~3,化学成分等各项指标均满足反应堆用核级碳化硼芯块的技术条件要求。