低周冲击加载评价硬质合金韧性的研究

通过低周冲击试验方法研究了几种不同WC晶粒度及Co相含量的硬质合金冲击疲劳性能并对其韧性和增韧效果进行了初步评估.试验结果表明:当WC晶粒度一定时,硬质合金的低周冲击疲劳性能随Co含量增加而提高;而对于相同Co含量的硬质合金,6.5μm晶粒度合金耐冲击疲劳性要强于1.8μm晶粒度合金.与常规韧性指标相比,低周冲击疲劳性能更有效地反映了硬质合金韧性及增韧作用.     

高能球磨-热压烧结制备定向排布板状WC硬质合金

采用高能球磨辅助特殊的热压烧结工艺制取定向排布板状WC硬质合金,研究了烧结温度和球磨时间对板状WC晶粒形成及其定向排布的影响.研究结果表明:烧结温度越高,越有利于晶粒粗化,形成大块板状WC晶粒;高能球磨中引入的缺陷是促进WC晶粒长径比提高的主要原因;WC晶粒的均匀性、粒径和长径比是影响其定向排布的主要因素.制备定向排布板状WC硬质合金是同时提高硬质合金硬度和韧性的有效方法.     

添加氧化镧WC-11Co-2.1TaC硬质合金的组织及性能

硬质合金的晶粒度和组织均匀性是制约其性能的关键因素。为了细化晶粒,改善组织,提高合金性能,采用粉末碳化、冷压烧结技术,以W、Co、Ta为原料,La_2O_3为添加剂,制备WC-11Co-2.1Ta C硬质合金,研究添加La_2O_3对硬质合金组织和力学性能的影响。结果表明:添加0.2%~0.4%La_2O_3可抑制WC-11Co-2.1Ta C硬质合金组织WC晶粒聚集生长,使组织均匀,WC相邻接度减小,WC/Co接触面积增大,提高抗弯强度;当La_2O_3添加量增加到0.6%时,合金组织偏聚,WC晶粒严重聚集生长,WC相邻接度增大,提高了硬质合金抵抗显微金刚石压头的刻入能力,增大了显微硬度。     

再生WC-Co粉与混合稀土制备YG8硬质合金存在的脱碳问题研究

以再生WC粉混合制备YG8为研究对象,通过对合金性能和组织进行检测,结果发现,稀土的添加并没有抑制脱碳现象的生成,相反在一定程度上还加剧了碳的脱除。此外,与原生WC粉末制备的硬质合金相比,再生粉末制备的硬质合金,合金样品组织中出现更为明显的脱碳现象,这主要归因于再生粉末本身晶粒尺寸分布不均,杂质含量偏高等缺点,使粉末在球磨过程中易吸附有害气体,并出现更多的孔隙、空洞等缺陷,为碳的氧化或扩散提供动力。     

含板状WC晶粒WC-10%Co硬质合金的组织和性能

采用板状WC单晶颗粒作为晶种制备含板状WC晶粒的WC-10%Co(质量分数)硬质合金,研究板状WC晶种的加入对WC-10%Co硬质合金显微组织和性能的影响。研究结果表明:加入板状晶种后,WC-10%Co合金中的WC晶粒具有明显的板状特征,且晶粒尺寸大于未加晶种的合金晶粒尺寸;少量晶种的加入对WC-10%Co合金密度无影响,而硬度和韧性都有所增加,特别是抗弯强度增加12.8%,断裂韧性提高46.9%。合金中WC晶粒形状的改变是硬度和韧性提高的主要因素。     

SPS预烧结制备超细晶梯度硬质合金

首先采用SPS预烧结和真空预烧结制备超细晶硬质合金,再经过梯度烧结使超细晶硬质合金表面形成梯度层,研究了不同预烧结方式对合金组织的影响,分析了预烧结后合金微观组织对超细晶硬质合金的梯度形成及晶粒生长的影响.结果表明,预烧结后合金的微观组织对梯度烧结后的梯度形成和晶粒生长有较大影响,经过SPS预烧结后的硬质合金进行梯度烧结后,可以获得梯度层厚度为 53μm,平均WC晶粒尺寸为0.3μm的超细晶梯度硬质合金.     

抑制硬质合金烧结中WC晶粒长大的研究

该文选择了VC和Cr3C2作为WC—Co硬质合金晶粒长大抑制剂，研究两种抑制剂加入量对合金组织、WC晶粒度和性能的影响以及抑制晶粒长大的机理．研究结果表明，VC和Cr3C2的加入十分有效地抑制了基体合金WC晶粒的长大，合金中的WC晶粒度随抑制剂加入量的增加而减小，可达到最小的WC晶粒度接近100nm,合金的硬度随抑制剂加入量增加而增加，但强度则下降。同时也会增加孔隙度，结果增加了脆性，降低了合金的强度．VC的有害影响比Cr3C2更大。     

亚微米-纳米晶粒WC-Co硬质合金烧结与组织

将用高能球磨法制取的亚微米-纳米晶粒WC-Co粉,采用脉冲电流在不同温度下加热烧结.结果表明,在1 200 ℃真空烧结3 min可以获得致密的块状亚微米-纳米晶粒WC-Co硬质合金,而WC晶粒无明显长大,其硬度高达HRA94.温度过低则组织疏松,过高则WC晶粒发生再结晶长大.     

碳化钨钢结硬质合金GJW50的微观组织分析

本文研究了碳化钨钢结硬质合金GJW50的微观组织。在电镜下观察到硬质相WC晶粒边界的溶解迹相和晶粒内的位错以及不同热处理状态钢基体的组织形态;通过x-射线物相分析结果表明,退火态合金的主要相是WC、α-Fe、M_3C和M_6C型复合碳化物;淬火高温回火态的主要相是WC、α-Fe和M_6C型复合碳化物;用扫描电镜和电子探针微区相成份分析结果证明,硬质相WC晶粒有局部溶解于钢基体,并发现GJW50合金组织中存在有“贫铁”和“富铁”两种类型的硬质相。     

WC晶粒度不同的双层硬质合金中的梯度结构

以晶粒度不同的2种WC粉末为原料,制备双层硬质合金试样.研究结果表明:在试样的层界面附近,出现过渡显微组织,其WC晶粒度、硬度呈现梯度分布,细晶层一侧的WC晶粒粗化,Co相平均自由程增大,硬度下降;粗晶层一侧的硬度上升;合金两侧的WC颗粒均处于非平衡状态.液相烧结时,界面两侧都有从外界吸入液态钴相以便使WC颗粒达到平衡状态的趋势,由于溶解-析出机制的作用,细晶侧的WC颗粒溶解后通过界面在粗晶侧的WC颗粒上析出,从而使粗晶侧的WC长大并达到平衡状态;与粗晶侧的WC相比,细晶侧的WC颗粒处于更加不稳定的状态,因此,粗晶侧的液态钴相流向细晶侧,使细晶侧的WC骨架发生重组而达到稳定状态.     

Solidification,microstructure, and mechanical properties of the as-cast ZRE1 magnesium alloy with different praseodymium contents

The influence of praseodymium(Pr) content on the solidification characteristics, microstructure, and mechanical properties of ZRE1 magnesium(Mg) cast alloy was investigated. The obtained solidification parameters showed that Pr strongly affected the solidification time, leading to refinement of the microstructure of the alloys. When the freezing time was reduced to approximately 52 s, the grain size decreased by 12%. Mg_(12)Zn(Ce,Pr) was formed as a new phase upon the addition of Pr and was detected via X-ray diffraction analysis. The addition of Pr led to a substantial improvement in mechanical properties, which was attributed to the formation of intermetallic compounds; the ultimate tensile strength and yield strength increased by approximately 10% and 13%, respectively. Pr addition also refined the microstructure, and the hardness was recovered. The results herein demonstrate that the mechanical properties of Mg alloys are strongly influenced by their microstructure characteristics, including the grain size, volume fraction, and distribution of intermetallic phases.     

Solidification,microstructure, and mechanical properties of the as-cast ZRE1 magnesium alloy with different praseodymium contents

The influence of praseodymium (Pr) content on the solidification characteristics, microstructure, and mechanical properties of ZRE1 magnesium (Mg) cast alloy was investigated. The obtained solidification parameters showed that Pr strongly affected the solidification time, leading to refinement of the microstructure of the alloys. When the freezing time was reduced to approximately 52 s, the grain size decreased by 12%. Mg₁₂Zn (Ce,Pr) was formed as a new phase upon the addition of Pr and was detected via X-ray diffraction analysis. The addition of Pr led to a substantial improvement in mechanical properties, which was attributed to the formation of intermetallic compounds; the ultimate tensile strength and yield strength increased by approximately 10% and 13%, respectively. Pr addition also refined the microstructure, and the hardness was recovered. The results herein demonstrate that the mechanical properties of Mg alloys are strongly influenced by their microstructure characteristics, including the grain size, volume fraction, and distribution of intermetallic phases.     

Ca对变形Mg-9Li-2Zn合金显微组织和机械性能的影响

实验熔制了Mg-9%Li-2%Zn(质量分数)合金并研究了添加质量分数为0.1%~0.5%的Ca对合金的影响.合金板材具有良好的冷加工性能,室温下可以轧成2 mm厚的薄板.研究了微量元素Ca对板材显微组织和机械性能的影响.室温下对板材进行拉伸测试,结果表明添加元素Ca能够提高合金的机械性能,当添加质量分数为0.1%的Ca时,板材的抗拉强度和延伸率分别提高了19%和6%,随着Ca含量的增加,强度略有提高而延伸率下降.通过显微观察可知,Ca对显微组织有细化作用,其中含Ca 0.1%时效果最明显.通过分析结果可知Ca在晶界处的吸附致使显微组织细化,进而影响了板材的机械性能.     

高扩孔钢变形奥氏体的连续冷却转变

研究了三种硅—锰系低碳钢变形奥氏体的连续冷却转变,分析了w(Si),w(Mn)对相变温度Ar3、转变组织及力学性能的影响.实验结果表明:w(Si)由0.50%增加到1.35%时,Ar3升高15~25℃,而w(Mn)由0.97%增加到1.43%时,Ar3降低30~50℃,锰对Ar3的影响效果强于硅;硅促进了高温等轴铁素体析出,抑制了贝氏体相变,而锰不仅细化了相变组织,还促进了贝氏体形成;w(Si),w(Mn)分别为0.56%和1.43%的钢在850℃变形后以30℃/s冷却,获得均匀、微细化的铁素体/贝氏体双相组织,抗拉强度可达到654 MPa.     

3.5Ni低温钢中Mn元素的强韧性作用研究

利用光学显微镜和电子探针对不同Mn含量3.5Ni低温钢的显微组织进行观察和分析,并研究了Mn元素对钢板热轧态、正火态及正火+回火态显微组织和力学性能的影响。结果表明,Mn含量的变化不影响组织的类型及晶粒的大小,提高低温钢中Mn元素含量可增加置换原子Mn的比例,增强低温钢的强度,但其带状组织更为明显;降低3.5Ni低温钢中Mn含量可使带状组织减少,有利于其低温韧性的提高;正火工艺能够有效地均化、细化钢板的显微组织,改善钢板的冲击韧性,且可明显降低材料韧脆转变温度。     

Formation of tough interlocking microstructures in silicon nitride ceramics by dynamic ripening

Ceramics based on Si(3)N(4) have been comprehensively studied and are widely used in structural applications. The development of an interlocking microstructure of elongated grains is vital to ensure that this family of ceramics have good damage tolerance. Until now this has been accomplished by heating the appropriate powder compacts to temperatures above 1,700 degrees C for extended periods. This procedure involves a necessary step of controlling the size and population of seeds added ex situ or formed in situ to ensure selective grain growth. Here we report the very fast (within minutes) in situ formation of a tough interlocking microstructure in Si(3)N(4)-based ceramics. The microstructures are obtained by a dynamic ripening mechanism, an anisotropic Ostwald ripening process that results from the rapid heating rate. The resulting microstructures are uniform and reproducible in terms of grain size distribution and mechanical properties, and are easily tailored by manipulating the kinetics. This process is very efficient and opens up new possibilities to optimize mechanical properties and cost-effectively manufacture ceramics.     

添加或未添加 Cu?Nb 的超低碳高强度钢焊接金属的显微组织和力学性能

Two types of ultralow carbon steel weld metals (with and without added Cu?Nb) were prepared using gas metal arc welding (GMAW) to investigate the correlation between the microstructure and mechanical properties of weld metals. The results of microstructure characterization showed that the weld metal without Cu?Nb was mainly composed of acicular ferrite (AF), lath bainite (LB), and granular bainite (GB). In contrast, adding Cu?Nb to the weld metal caused an evident transformation of martensite and grain coarsening. Both weld metals had a high tensile strength (more than 950 MPa) and more than 17% elongation; however, their values of toughness deviated greatly, with a difference of approximately 40 J at ?50°C. Analysis of the morphologies of the fracture surfaces and secondary cracks further revealed the correlation between the microstructure and mechanical properties. The effects of adding Cu and Nb on the microstructure and mechanical properties of the weld metal are discussed; the indication is that adding Cu?Nb increases the hardenability and grain size of the weld metal and thus deteriorates the toughness.     

C颗粒对Cp/AZ91D复合材料铸态显微组织的影响

通过复合铸造工艺制备了C_p/AZ91D复合材料，研究了C颗粒含量和保温时间等参数对该复合材料显微组织和力学性能的影响。结果表明，与保温时间相比，C_p的晶粒细化作用更为显著。当添加C_p质量分数为1.5%，保温时间15 min时，C_p/AZ91D复合材料铸锭平均晶粒尺寸由176 μm降低至32 μm，组织整体细化均匀，增强相C颗粒在复合材料基体中均匀分布，并且硬度值最高，达到89.07 HV。     

C颗粒对Cp /AZ91D复合材料铸态显微组织的影响

通过复合铸造工艺制备了C_p/AZ91D复合材料，研究了C颗粒含量和保温时间等参数对该复合材料显微组织和力学性能的影响。结果表明，与保温时间相比，C_p的晶粒细化作用更为显著。当添加C_p质量分数为1.5%，保温时间15 min时，C_p/AZ91D复合材料铸锭平均晶粒尺寸由176 μm降低至32 μm，组织整体细化均匀，增强相C颗粒在复合材料基体中均匀分布，并且硬度值最高，达到89.07 HV。     

Metallographic etching and microstructure characterization of NiCrMoV rotor steels for nuclear power

The grain size of prior austenite has a distinct influence on the microstructure and final mechanical properties of steels. Thus, it is significant to clearly reveal the grain boundaries and therefore to precisely characterize the grain size of prior austenite. For NiCrMoV rotor steels quenched and tempered at high temperature, it is really difficult to display the grain boundaries of prior austenite clearly, which limits a further study on the correlation between the properties and the corresponding microstructure. In this paper, an effective etchant was put forward and further optimized. Experimental results indicated that this agent was effective to show the details of grain boundaries, which help analyze fatigue crack details along the propagation path. The optimized corrosion agent is successful to observe the microstructure characteristics and expected to help analyze the effect of microstructure for a further study on the mechanical properties of NiCrMoV rotor steels used in the field of nuclear power.