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211.
《Ceramics International》2016,42(12):13497-13506
Si3N4/(W, Ti)C graded nano-composite ceramic tool materials with different thickness ratios and number of layers were fabricated by hot pressing technology. The flexural strength, fracture toughness and hardness of the sintered composites were tested and the microstructure and indention cracks were observed. The experiment results showed that the five-layer graded nano-composites with a thickness ratio of 0.2, which were sintered under a pressure of 30 MPa at 1700 °C in vacuum condition for 45 min, had the optimum comprehensive mechanical properties with a flexural strength of 1080.3 MPa, a hardness of 17.64 GPa, and a fracture toughness of 10.87 MPa·m1/2. The formation of elongated β-Si3N4 grains contributes to the favorable mechanical properties. The graded structure can induce residual compressive stress in the surface layer and enhance the mechanical properties. The strengthening and toughening mechanisms are a synergistic effect of intergranular and transgranular fracture, crack bridging and deflection. 相似文献
212.
本工作研究了富CoCr含量的CoCrNi基中熵合金的高温力学性能及其变形机制。研究发现,经过热锻以及时效热处理,成分为Co33.3Cr30.6Ni26.1Al5Ti5 (at%)中熵合金在600~800℃的温度范围内具有优异的瞬时拉伸性能。特别是,在700℃条件下出现反常屈服,屈服强度高达为944 MPa,拉伸塑性为16%,优于大多数镍基以及钴基高温合金。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和三维原子探针(3D-APT)等手段,发现高体积分数的多主元γ′[(Ni,Co,Cr)3(Al,Ti)]相的有序强化以及晶界处生成的多主元富(Co,Cr)面心立方相(fcc)结构相引起的晶界强化是该合金在高温条件下实现强韧化的主要因素。 相似文献
213.
Magnesium (Mg) and its alloys have broad application prospects in the fields such as biomedical materials and automobile manufacturing. A micro-alloyed Mg-2.0Nd-0.2Sr (wt.%) magnesium alloy is designed and obtained through semicontinuous casting. The evolution of microstructures and tensile properties are investigated with different heat treatments and extrusion treatments. The grain sizes decrease significantly after extrusion, thus changing the fracture mode during the tensile testing process. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of the properly processed extrusion alloy (referred to as MNS-E2) reach to 247 MPa, 228 MPa and 24%, respectively. The dramatical improvement of mechanical properties results from the refined grains and interactions between dislocations and precipitates. Some nanoparticle bands blocking the slippage and movement of dislocations are also found in the MNS-E2 alloy. The above causes combined result in an integrated effect of grain boundary strengthening, dislocation strengthening, precipitation strengthening and nanoparticle band strengthening. The contribution of strengthening mechanisms of MNS-E2 alloy consists of grain boundary with around 96 MPa, dislocations with around 3.4 MPa, precipitation strengthening with around 45 MPa and the nanoparticle band with around 18 MPa, respectively. 相似文献
214.
采用MTS-CMT5105电子万能试验机,在温度为250~400℃、初始应变速率为10-4~10-1s-1,最大变形量为40%的条件下,对铸态Mg-2.5Sn(wt.%)和Mg-2.5Sn-0.2Y(wt.%)合金进行压缩变形。结合真应力-应变曲线、峰值应力、显微组织、本构方程、DMM加工图,研究了微量Y(0.2 wt.%)对铸造Mg-Sn合金热变形行为的影响。结果表明:微量Y的添加,在较低应变速率时,会使Mg-Sn合金热压缩峰值应力增加30%以上;但在较高应变速率时,却对其影响不大。会改变合金塑性变形机制的控制方式,即由扩散控制变为位错的滑移和攀移。会抑制动态再结晶。会降低功率耗散系数,扩大加工失稳区。 相似文献
215.
216.
执行《煤矿安全规程》,保证安全供电,对变压器、开关、线路做到专用,装备风电闭锁与瓦斯电闭锁装置,确保安全生产。 相似文献
217.
山西潞安环保能源开发股份有限公司王庄煤矿在 6 10 5工作面使用DSF型单向锁对MXA - 30 0型采煤机的调高系统进行了改造 ,很好地预防了其在运转过程中常出现的摇臂下滑、自落现象 ,为工作面正常生产创造了条件。 相似文献
218.
219.
Lactic acid bacteria (LAB) starter cultures can be processed by many drying techniques, among which spray drying has great potential. However, injuries of LAB during spray drying lead to a low survival rate. The microbial injuries of LAB during spray drying are specifically induced by dehydration inactivation, thermal inactivation, and balance between the two. To reduce the drying temperature, new drying techniques based on spray drying were tried; that is, low-temperature vacuum–spray drying and spray–freeze drying. 相似文献
220.
《Journal of the European Ceramic Society》2014,34(14):3319-3328
Silicon nitride materials containing 1–5 wt% of hexagonal boron nitride (micro-sized or nano-sized) were prepared by hot-isostatic pressing at 1700 °C for 3 h. Effect of hBN content on microstructure, mechanical and tribological properties has been investigated. As expected, the increase of hBN content resulted in a sharp decrease of hardness, elastic modulus and bending strength of Si3N4/BN composites. In addition, the fracture toughness of Si3N4/micro BN composites was enhanced comparing to monolithic Si3N4 because of toughening mechanisms in the form of crack deflection, crack branching and pullout of large BN platelets. The friction coefficient was not influenced by BN addition to Si3N4/BN ceramics. An improvement of wear resistance (one order of magnitude) was observed when the micro hBN powder was added to Si3N4 matrix. Mechanical wear (micro-failure) and humidity-driven tribochemical reaction were found as main wear mechanisms in all studied materials. 相似文献