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.

Elastic and thermodynamic properties of vanadium nitride under pressure and the effect of metallic bonding on its hardness

By the particle-swarm optimization method, it is predicted that tetragonal P42mc, 141md, and orthorhombic Amm2 phases of vanadium nitride （VN） are energetically more stable than NaCl-type structure at 0 K. The enthalpies of the predicted three new VN phases, along with WC, NaC1, AsNi, CsCl type structures, are calculated each as a function of pressure. It is found that VN exhibits the WC-to-CsCl type phase transition at 256 GPa. For the considered seven crystal- lographic VN phases, the structures, elastic constants, bulk moduli, shear moduli, and Debye temperatures are investigated. Our calculated equilibrium structural parameters are in very good agreement with the available experimental results and the previous theoretical results for the NaC1 phase. The Debye temperatures of VN predicted three novel phases, which are all higher than those of the remaining structures. The elastic constants, thermodynamic properties, and elastic anisotropies of VN under pressure are obtained and the mechanical stabilities are analyzed in detail based on the mechanical stability criteria. Moreover, the effect of metallic bonding on the hardness of VN is also investigated, which shows that VNs in P42mc, 141md, and Amm2 phases are potential superhard phases. Further investigation on the experimental level is highly recommended to confirm our calculations presented in this paper.

Hard Magnetic Properties of Sm-Fe-C Based Alloys Prepared by Mechanical Alloying

The structure and magnetic properties of SmyFe100-1.5yC0.5y(y=8～20) alloys prepared by mechanical alloying (MA) from Sm, Fe and graphite have been investigated systematically. In order to improve hard magnetic properties of the alloys prepared by mechanical alloying, a new method consisting of re-milling and re-annealing was developed. After being re-milled and re-annealed, the Curie temperature TC of the Sm-Fe-C alloys changes. The TC of 2:17 phase increases, whereas the TC of 2:14:1 phase decreases. After being re-annealed at low temperatures, the grain sizes of hard phases are smaller than those in the alloys annealed at high temperatures. The effects of Co or Ti substitution for Fe are studied.

Analysis of the elastic-plastic indentation properties of materials with varying ratio of hardness to Young’s modulus

The elastic-plastic indentation properties of materials with varying ratio of hardness to Young’s modulus(H/E) were analyzed with the finite element method. And the indentation stress fields of materials with varying ratio H/E on the surface were studied by the experiment. The results show that the penetration depth, contact radius, plastic pile-up and the degree of elastic recovery depend strongly on the ratio H/E. Moreover, graphs were established to describe the relationship between the elastic-plastic indentation parameters and H/E. The established graphs can be used to predict the H/E of materials when compared with experimental data.

Theoretical investigation on the electronic structure,elastic properties, and intrinsic hardness of Si2N20

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli （bulk modulus, Young’s mod-ulus, and shear modulus） are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.

Use of Shore Hardness Tests for In-Process Properties Estimation/Monitoring of Silicone Rubbers

Casting is an important rubber manufacturing process for both production and material developments. A quick and flexible way of testing the constitutive materials properties of rubber products is very important for optimising the processing parameters and quality control. In many cases, standard tests such as tensile or compression tests are time consuming and require a large volume of materials. This work reports some recent work in using a combined numerical and experimental approach to characterise the properties of rubber materials during a casting process. Durometer shore hardness is used to test silicone rubbers (as a model material) with different compositions on different moulding planes and the linear elastic property is estimated from the hardnesses. The predicted properties are systematically compared with the experimental tests on hard and soft silicone rubber samples with different compositions. The work shows that shore hardness can be used as an effective way to monitor the materials properties during amoulding process for process optimisation and quality control.

高温后冷却方式对玄武岩纤维混凝土力学性能的影响

高温处理后混凝土力学性能是工程建设中评价混凝土结构安全性能的重要指标之一。对不同玄武岩纤维(BF)掺量混凝土的力学性能进行了测试,将最优掺量的玄武岩纤维混凝土(BFRC)与普通混凝土(OC)进行高温处理(200、400、600、800℃),研究不同冷却方式(自然冷却和喷水冷却)对高温后BFRC性能劣化的影响,分析BFRC在不同温度和冷却方式下的力学性能变化规律。结果表明,当BF掺量为0.05%(体积分数)时,BFRC抗压强度、劈裂抗拉强度达到最大值,分别为50.2、3.5 MPa,较OC分别提高了14.87%、34.62%。BF的掺入能够有效增加混凝土的韧性以及抵抗开裂变形的能力。随着温度增加,BFRC试件的弹性模量减小但始终大于OC试件。同一冷却方式下OC的峰值应变均大于BFRC,不同冷却方式下的延性指数较常温均有所提高。

碳纳米管增韧Al-Mg合金复合材料的制备与性能研究

选择碳纳米管为增强相,通过搅拌铸造法制备了碳纳米管增韧Al-Mg合金复合材料,研究了碳纳米管的添加量对复合材料力学性能、微观组织以及韧性的影响,并探究了碳纳米管对Al-Mg合金的增韧机理。结果表明,掺入适量的碳纳米管后细化了Al-Mg合金复合材料的晶粒,晶粒尺寸约为80μm,当碳纳米管的添加量为0.8%(质量分数)时,复合材料的断口形貌最均匀。随着碳纳米管添加量的增大,复合材料的抗拉强度、断裂伸长率、硬度均表现出先增大后降低的趋势,当碳纳米管的添加量为0.8%(质量分数)时,抗拉强度、断裂伸长率和硬度均达到了最大值,分别为208.6 MPa、15.8%和53.1 HB。适量碳纳米管的添加显著改善了Al-Mg合金的韧性,使断裂延伸率逐渐增大,屈服阶段延长,韧性得到提高,这是因为适量的碳纳米管添加后能够与合金发生较好的结合,并贯穿于合金的裂纹中,发挥出了桥联作用,阻碍了裂纹的萌生和扩展,从而改善了Al-Mg合金复合材料的韧性,延缓了合金的失效过程,延长了合金的屈服阶段。综上分析可知,碳纳米管的最佳添加量为0.8%(质量分数)。

不同温度条件下相变石蜡力学性能分析

对3种不同相变温度的石蜡材料(PCM-28、PCM-18和PCM-10)在不同温度下的基本力学性能参数进行了系统的压缩实验,计算出对应的弹性模量和泊松比。结果表明:PCM-18和PCM-10的抗压强度随温度的降低而有所提高,但PCM-28的抗压强度随温度的降低反而呈现出下降趋势。在单轴压缩条件下PCM-28和PCM-18的应力-应变曲线主要经历了压实阶段、弹性变形阶段、裂纹扩展阶段和裂纹后破坏阶段4个明显阶段,最终表现为脆性破坏。PCM-10在经历压实阶段和弹性变形阶段后进入塑性阶段,曲线发展近似水平,且整个过程无明显裂纹出现。

煤体微观力学特性的纳米压痕实验研究

煤体力学性质的测定与研究对煤炭高效开采和灾害预防具有重要的理论价值。煤较为松软破碎,强度较低,难以制备标准的力学测试煤样,也无法回收利用从而进行重复测试。亟需探索新的力学测试方法完善煤的力学特性研究。纳米压痕技术可以测定小尺度煤体微观力学特性,具有样品易制作、实验快速、样品无损的特点。结合矿物组分测试、形貌扫描和纳米压痕实验,研究了4种煤的物性特征及微观力学性质。结果表明,实验煤样矿物类别主要包括非晶态有机质和黏土、石英和碳酸盐类矿物,不同煤的矿物组分有显著差异。煤的3D形貌图显示不同煤表面粗糙度差异明显,煤中矿物分布具有显著非均质性。纳米压痕实验结果表明:①煤样中石英和碳酸盐类矿物质量分数越高,会导致煤样表面力学性质越强,压痕深度越小;②煤样表面的组分越复杂,煤的非均质性越明显,表面微观力学性质分布的离散程度越高;③煤的煤阶越高,变质程度越高,外部孔隙越发育,导致断裂韧度提高;④对压痕试验结果进行拟合,发现弹性模量与坚固性系数、弹性模量与断裂韧度均具有明显的线性关系,并且弹性模量与断裂韧度的线性关系受峰值载荷的影响。

硬岩顶板切顶留巷围岩变形分区补强控制研究

【目的】森达源煤矿传统的宽煤柱开采方式导致采掘接续紧张,并引发严重的围岩变形问题。切顶留巷技术可优化巷道支护条件,提高采煤效率,促进煤矿高效安全生产。【方法】以1号煤层的10101工作面为研究对象,运用FLAC 3D数值模拟软件,深入探究了切顶高度、切顶角度、注浆加固深度对巷道掘进、预裂切顶和切顶留巷过程中煤帮内部、采空区及顶板应力变形特性的影响。确定出最佳切顶留巷方案。在此基础上,进一步模拟分析工作面前后不同区域的围岩受力变形情况。提出回采工作面前方0~30 m内为超前补强区,采取“高预应力锚索+单体配合铰接顶梁”的联合支护。后方0~100 m内为滞后补强区,采用“工字钢+单体支柱”联合支护,同时对矸石帮实施注浆加固。通过工程应用验证了区分补强控制变形措施的有效性。【结果】结果显示:最佳切顶留巷方案为切顶高度6 m,切顶角度15°,矸石帮注浆深度1 m。此方案下,10101工作面的巷道顶底板的最终变形量为155 mm,两帮的为84 mm,均符合矿井使用要求,验证了切顶留巷技术具有良好效果。【结论】结果表明:切顶留巷技术能有效解决传统宽煤柱开采方式中存在的围岩变形问题。然而,该技术的实施受切顶高度、切顶角度和矸石帮注浆深度等因素的影响较大,需结合数值模拟和现场状况进行具体确定。总体上,切顶留巷技术和分区补强控制措施对围岩变形的控制效果显著,为类似条件下的煤矿开采提供了宝贵的经验借鉴,因而具有广阔的应用前景。

山药综合力学性能测试的研究

为了获得山药在不同加载速度下的力学性能参数,采用微机控制电子式万能试验机(WDW-5E)对“牛腿”山药进行了不同加载速度下的压缩、弯曲、拉伸试验。测得不同加载速度下的轴向抗压强度、轴向弹性模量、径向抗压强度、径向弹性模量、抗弯强度、抗弯弹性模量、抗拉强度、抗拉弹性模量,由此得出山药弯曲断裂载荷在40~140 N之间;轴向和径向的弹性模量随加载速度增大而增大;加载速度对山药其他力学性能参数无显著影响。通过对山药的综合力学性能的研究,能够在收获时调整机具工作参数,降低机械对山药的损伤,为实现山药智能化机械采收提供参考。

Influence of Zr content on microstructure and mechanical properties of implant Ti-35Nb-4Sn-6Mo-xZr alloys

The influence of Zr content on the microstructure and mechanical properties of implant Ti-35Nb-4Sn-6Mo-xZr （x=0, 3, 6, 9, 12, 15; mass fraction） alloys was investigated. It is shown that Ti-35Nb-4Sn-6Mo-xZr alloys appear to have equiaxed single β microstructure after solution treatment at 1023 K. It is found that the grains are refined first and then coarsened with the increase of Zr content. It is also found that Zr element added to titanium alloys has both the solution strengthening and fine-grain strengthening effect, and affects the lattice parameters. With increasing the Zr content of the alloys, the strength increases, the elongation decreases, whereas the elastic modulus firstly increases and then decreases. The mechanical properties of Ti-35Nb-4Sn-6Mo-9Zr alloy are as follows： σb=785 MPa, δ=11%, E=68 GPa, which is more suitable for acting as human implant materials compared to the traditional implant Ti-6Al-4V alloy.

不同增强方向的带支柱体心立方点阵及其填充结构的压缩力学性能分析

为研究不同增强方向的带支柱体心立方点阵及其填充结构的压缩力学性能,制备了硅橡胶填充点阵结构试验件。通过试验和仿真方法研究了硅橡胶填充BCC1或BCC2(加载方向分别与带支柱体心立方点阵的支柱杆方向相同或垂直)两种点阵结构的压缩力学性能,并采用铁摩辛柯梁理论和极限载荷法分析了两种点阵结构的等效弹性模量和压缩平台应力。结果表明:提出的理论模型能够很好地预测两种点阵结构的等效弹性模量和压缩平台应力。经过填充后两种点阵结构的压缩强度和吸能性能均会得到增强,BCC2结构的增强效果更加显著。对于BCC1点阵结构,填充提高了其内部杆件的承载力;而对于BCC2点阵结构,填充减小了其“V”形剪切带附近的杆件弯曲变形。随着点阵结构半径的增大,两种结构的吸能耦合因子均先增大后减小,而BCC1型结构的吸能耦合因子变化更明显。

金属/高熵合金纳米多层膜的制备、微观结构及力学性能研究进展

通过表面防护涂层技术制备综合力学性能与摩擦性能优异的涂层材料,对降低构件因碰撞摩擦磨损所引起的损伤失效问题十分重要。相较于单层膜结构防护涂层,金属纳米多层膜涂层材料由于其微观组织结构的独特性与可控性,表现出优异的服役特性,且其综合性能可通过结合新组元或界面调控得到进一步提高,因此该类材料受到了广泛关注。新颖的成分设计理念使得高熵合金具有独特的四大效应,即高熵效应、晶格畸变效应、迟滞扩散效应和性能鸡尾酒效应,进而呈现出良好的综合性能。因此,在传统的双金属纳米多层膜结构材料中引入高熵合金组元,形成金属/高熵合金纳米多层膜,有望突破传统金属纳米多层膜的性能局限,极大地提高多层膜结构材料的力学性能。从功能基元序构的视角,围绕近几年金属/高熵合金纳米多层膜的相关研究,首先介绍了其制备方法和工艺原理,针对功能基元微观结构特征,从晶粒形貌、界面结构、组元成分等方面进行了阐释,在此基础上论述了其力学行为以及相应的内在机制,并提出了调控金属/高熵合金纳米多层膜力学性能的优化策略,最后对金属/高熵合金纳米多层膜的未来研究方向和面临的挑战进行展望。

V-5Cr-5Ti合金弹性和力学性质的第一性原理研究

V-5Cr-5Ti合金作为核聚变堆第一包层的主要候选结构材料之一,但对其力学性质的理论研究相对较少.采用随机固溶体模型,利用第一性原理方法计算出V-5Cr-5Ti合金的弹性常数、体模量、剪切模量、杨氏模量、泊松比和柯西压力等,并与计算出的纯钒的相关数值进行对比,结果表明V-5Cr-5Ti合金具有良好的塑性和强度,但其塑性要略低于纯钒的.并对加入氧原子后的V-5Cr-5Ti合金进行了相关计算,通过对比计算结果发现,由于氧原子的加入,使V-5Cr-5Ti合金的塑性和强度都出现了不同程度的降低.最后对V-5Cr-5Ti合金和纯钒的理论强度进行了计算,并绘制出两者的应力-应变关系图,通过对比再次验证了上面的结论.

IPDI型高硬度单组分聚脲的制备及性能研究

为满足高硬度和轻量化的需求,以异氰酸酯为硬段,多元醇和端羟基聚醚为软段,潜固化剂为扩链剂,并加入催化剂、水解促进剂和其他外加剂等制备了IPDI型高硬度单组分聚脲。通过对固化时间、黏度、硬度、力学性能等进行测试,研究了原料组成和配方设计对单组分聚脲性能的影响;采用红外光谱表征了该涂层的微观结构和氢键形成情况,并通过水接触角和吸水率试验评估其防水性能。结果表明:随—NCO含量的增加,单组分聚脲的固化时间和力学性能均逐渐提高,特别是以聚酯多元醇为软段制备的涂层综合性能表现更为优异。此外,涂层力学性能随潜固化剂用量的增加呈先增大后减小的趋势,N—H和C=O吸收峰的偏移表明了涂层中有氢键形成。所制备的IPDI型高硬度单组分聚脲能够满足目标应用需求。

采用纳米氧化铝制备高弹性模量超高性能混凝土的可行性研究

纳米材料具有粒径小、比表面积大、化学活性高等独特性能,能够提升水泥基材料的力学性能和在恶劣环境下的耐久性,在水泥基材料领域具有广阔的应用前景。弹性模量是超高性能混凝土(UHPC)的重要力学参数之一。虽然目前UHPC的抗压强度得到了大幅提升,但是其弹性模量并未随抗压强度同幅度增长。为了探究采用纳米氧化铝(NA)制备高弹性模量UHPC的可行性,本工作利用MAA (Modified Andreasen and Andersen)模型设计UHPC初始配合比,研究不同掺量的NA对UHPC工作性能、力学性能和耐久性能的影响。此外,本工作还探究了NA对UHPC微观孔结构和微观力学性能的影响。研究表明:(1)NA能使UHPC的28 d抗折强度、抗压强度、弹性模量分别提高8.23%~16.31%、8.04%~26.39%、9.44%~16.55%;(2)NA能使UHPC的干缩、氯离子迁移系数分别降低2.54%~13.01%、8.21%~17.28%;(3)NA能够优化UHPC的孔结构,提高其浆体弹性模量;(4)综合考虑NA对UHPC工作性能、力学性能和耐久性能的影响,NA在UHPC中的优选掺量为1.0%。本工作的研究结果对利用NA制备高弹性模量的UHPC具有指导意义。

修复材料与牙体组织力学适配性的研究进展

牙齿作为发挥咀嚼功能的主要器官,可承受无数次功能性接触,这与它的力学性能和组织结构密切相关。牙釉质和牙本质的硬度较高,并且它们具有梯度化的结构,这使得牙齿既能承受咬合力,又不致轻易折裂。当牙体组织缺损时,往往需要全冠修复体来恢复牙齿正常的形态与功能。常用的全冠修复材料有金属材料、陶瓷材料以及最近兴起的聚醚醚酮材料。金属材料在美学方面存在一定劣势,目前在临床上应用相对较少。不同组成成分的陶瓷材料在性能及美学上的表现有所差异,但弹性模量与硬度过高,在力学性能方面都超过了牙体组织,与牙体组织学力学性能不匹配。与此不同,聚醚醚酮材料的弹性模量低于牙体组织,与骨组织相似,但通过纤维增强等方式能够提高它的性能。当修复材料与牙体组织的力学性能并不完全适配时,两者之间的界面往往形成潜在的薄弱环节,最终影响修复的稳定性和长期效果。本文介绍了牙釉质和牙本质的力学性能以及相对应的结构特点,并在此基础上,分析现有修复材料的优势与局限性,进一步探究口腔全冠仿生设计的可能性。

氢键/二硫键协同的室温修复聚氨酯的制备及性能研究

自修复材料作为一类新兴的智能材料,具有广泛的应用前景,然而此类材料难以兼具良好的力学性能与自修复能力。以聚四氢呋喃(PTMEG)为软段、异佛尔酮二异氰酸酯(IPDI)和双(4-羟苯基)二硫醚(4-HD)为扩链剂共同构成硬段,通过两步扩链反应制备了室温自修复聚氨酯(PUHD),并分别研究了单体配比与扩链剂的分子结构对PUHD的力学与自修复性能的影响。结果表明:当R值(R=[IPDI]/[PTMEG])为1.5时,PUHD的综合性能最佳,拉伸强度、断裂伸长率与韧性分别为7.53 MPa、1447.80%与31.98 MJ/m^(3)。PUHD-1.5具有良好的流变性能,在25与60℃下的特征弛豫时间分别为23.45与7.10 min,在25℃下修复6 h,断裂伸长率与拉伸强度的修复效率分别为95.29%和89.95%。扩链剂的分子结构对PUHD的自修复性能有显著影响,弱氢键作用与松散堆积的硬段有利于提高PUHD的自修复性能。