Fe-Cu-Mn-C合金的性能与烧结行为

以FeMn合金粉末的形式在铁基合金粉末中添加Mn元素,退火后得到Fe-Cu-Mn部分预合金粉末,采用模壁润滑温压工艺制备Fe-Cu-Mn-C合金,通过对合金密度与硬度的测定以及形貌观察,研究Fe-Cu-Mn-C粉末的压制与烧结行为,以及Mn含量对合金密度和力学性能的影响。结果表明,通过退火处理实现部分预合金扩散而得到的Fe-Cu-Mn粉末具有很好的压制性能,Fe-2Cu-0.5Mn-0.9C压坯密度达到7.37 g/cm3,烧结密度为7.33 g/cm3;添加适量Mn能有效提升铁基合金的力学性能,其中Fe-2Cu-0.5Mn-0.9C合金的性能最佳,抗拉强度达到715 MPa;随Mn含量增加,合金的孔隙增多、密度下降,导致强度和硬度下降。合金的局部氧化对性能产生一定的负面影响。Mn含量对合金组织影响不大,Fe-2Cu-Mn-0.9C合金呈现混合显微组织,由铁素体、珠光体和少量贝氏体构成。Mn的蒸发与凝聚是Fe-Cu-Mn-C的烧结机制。     

Cr的添加方式与含量对粉末冶金烧结钢组织及力学性能的影响

在Fe-1.75Ni-1.5Cu-0.5Mo-0.6C粉末中,分别以添加430L不锈钢粉和CrFe合金粉的方式加入Cr元素,采用高温烧结硬化工艺制备含铬烧结钢Fe-1.75Ni-1.5Cu-xCr-0.5Mo-0.6C(x=0.5,1.0,1.5),研究铬的添加方式与含量对烧结钢组织与力学性能的影响。结果表明,与添加CrFe合金粉的方式相比,采用添加430L不锈钢粉的方式时,Cr的强化效果更好。采用该方式制备的含Cr烧结钢,随Cr含量增加,抗拉强度先上升后下降,伸长率不断下降,硬度不断提高,含铬量1.0%的材料具有良好的综合性能,生坯密度和烧结密度分别为7.18g/cm3和7.20g/cm3,抗拉强度、伸长率和硬度分别达到910MPa、2.0%和30HRC;烧结钢组织主要以珠光体、贝氏体和马氏体为主的混合组织;烧结钢的拉伸断裂以韧–脆混合断裂为主。     

碳含量及烧结温度对MIM 4340合金钢组织及力学性能的影响

采用注射成形工艺制备4340低合金钢,研究碳含量与烧结温度及热处理工艺对合金钢显微组织和力学性能的影响。结果表明:通过添加德国巴斯夫还原型羰基铁粉(CN)及改进型羰基铁粉(OM)的方式,分别配制不同碳含量的混合粉末,并经1 280～1 320℃保温2 h烧结后,质量分数为0.50%碳含量的样品最接近标准碳含量。烧结密度随碳含量的升高先减小后增大,随烧结温度升高而增大。烧结态显微组织由铁素体(α-Fe)、珠光体(铁素体+渗碳体Fe_3C)和贝氏体组成,抗拉强度和伸长率为762.16～1 032.03 MPa和5.25%～8.62%。0.50%碳含量、1 300℃烧结态4340合金钢样品经850℃保温0.5 h油冷及400℃保温2 h回火热处理后得到最佳力学性能,抗拉强度和伸长率达到1 510.24 MPa和4.30%,硬度为40.0 HRC。     

还原铁粉对Fe-1.1Ni-0.5Mo-0.5Cr合金组织与性能的影响

在惰性气体雾化法制备的Fe-1.1Ni-0.5Mo-0.5Cr预合金粉末中添加1.5％的Cu粉和0.6％的C粉(均为质量分数)以及还原铁粉(添加量分别为0、10％、20％和30％),混合均匀后在600 MPa压力下模压,在1 180℃烧结1h.烧结合金经180℃/1h回火处理后,进行密度、硬度、拉伸力学性能检测以及显微...     

微细Cr-Fe合金粉对粉末冶金钢组织与性能的影响

在Fe-0.5Mo预合金粉末中加入平均粒径为4.65μm的Fe Cr55C600高碳Cr-Fe合金粉末,于1 200℃,采用烧结硬化工艺制备Fe-Cr-Mo粉末冶金合金钢。结果表明:随着Cr-Fe合金粉末量的增加,合金烧结试样的硬度增加,强度增加,合金的显微组织以贝氏体为主。当添加微细颗粒的Cr-Fe合金粉末,使Cr质量分数达到1.7%时,合金烧结试样的综合性能达到最优,抗拉强度为1 210 MPa,硬度为30 HRC,显微组织主要为细小的下贝氏体和马氏体,此时合金中Cr/C质量比约为1.54。     

锰源粉末对Fe-Mn-C烧结钢组织和力学性能的影响

以电解锰粉和Fe-76% Mn粉末（质量分数）为原料,在600℃和70% N₂+30% H₂混合气体（体积分数）管式炉中氮化得到三种抗氧化含氮锰源粉末（Mn-3% N、Mn-5% N和FeMn-3% N,质量分数）,研究锰含量以及锰源粉末种类对压制烧结Fe-Mn-C烧结钢组织和力学性能的影响。研究表明:使用氮化锰源粉末制备的Fe-Mn-C烧结钢的力学性能明显优于采用电解锰粉为原料制备的同类材料,随着锰源粉末中N含量的升高,烧结钢烧结膨胀率减小,对合金的强化作用增加。以Mn-5% N作为锰源制备的Fe-2Mn-0.5C烧结钢,其拉伸强度为576 MPa,断后延伸率为3.8%,与电解锰粉为锰源相比,烧结钢的拉伸强度和断后延伸率分别提升了29%和123%。使用氮化锰粉作为锰源的烧结钢内孔隙数量减小,珠光体增多,片层间距降低。     

碳含量对注射成形HK30不锈钢显微组织与力学性能的影响

针对实际生产中注射成形HK30不锈钢碳含量较高导致其性能下降的问题,本研究在喂料中添加石墨来改变注射成形HK30奥氏体不锈钢的碳含量,研究碳含量(质量分数,下同)对HK30不锈钢显微组织与力学性能的影响。结果表明,随碳含量从0.02%增加至0.49%,HK30奥氏体不锈钢的氧含量降低,材料的孔隙减少,相对密度、硬度和抗拉强度都提高;随碳含量增加,不锈钢晶界处逐渐析出M23C6型碳化物,少量晶界碳化物的析出能强化晶界,使材料硬度与强度都显著提高,但碳含量从0.18%增加至0.49%,烧结阶段液相量大幅度增加,材料出现过烧,并且晶界碳化物异常长大,达到3~5μm,材料的伸长率显著减小到26%。当碳含量控制在0.18%时材料性能最优,硬度(HV)达到162.81,相对密度为96.4%,抗拉强度和伸长率分别为589.96 MPa和45.7%。     

铜含量对高碳TWIP钢组织和力学性能的影响

 采用真空熔炼法制备了Fe-20Mn-XCu-1.3C系高强度高塑性合金钢。通过单向拉伸试验和OM观察,研究了铜含量的变化对该合金微观组织和力学性能的影响。结果表明：Fe-20Mn-XCu-1.3C系合金拉伸变形前后均为单相奥氏体组织。随着铜含量的增加,合金的屈服强度和伸长率提高,而抗拉强度降低,Fe-20Mn-3.0Cu-1.3C合金的抗拉强度为1256MPa,伸长率为77.6%,强塑积达到97465.6MPa·%,具有优异的综合力学性能。铜含量的增加提高合金的层错能,推迟了变形过程中孪晶的形成并降低了孪晶的形成速率,使位错滑移更容易发生。Fe-20Mn-XCu-1.2C系合金具有较高的加工硬化速率水平,其加工硬化速率随着铜含量的增加而降低。     

Sn含量对粉末冶金304不锈钢组织和性能的影响北大核心

采用真空烧结制备了304奥氏体粉末冶金不锈钢,研究了不同Sn含量对粉末冶金304不锈钢材料显微组织、密度、抗拉强度和耐腐蚀性能的影响。结果表明:在烧结温度1300℃的条件下,随着Sn的添加量增加,组织中的孔隙数量减少,孔隙尺寸减小且分布均匀,不规则的大孔隙逐渐变为球形的小孔隙,试样具有最大的密度7.308 g/cm^(3)。当Sn的添加量为2%时,烧结试样断口的韧窝分布均匀,孔隙发生球化,孔隙较小且尺寸均匀,韧窝之间以网状相连,此时力学性能达到最优,硬度和抗拉强度分别达到62.23HRB和363.34 MPa。继续增大Sn的添加量,由于密度下降,力学性能也随之下降,断口中韧窝尺寸增大且出现不规则的形状。电化学实验表明,随着Sn含量增加到2%,304不锈钢的耐蚀性先增大后减小。     

Mn含量对粉末冶金铁铜碳低合金钢组织与力学性能的影响

采用铜粉、石墨粉和铁粉为原料,以Fe-74.8Mn-6.9C中间合金粉的形式加入Mn元素,制备粉末冶金Fe-x Mn-(2-x)Cu-0.3C(x=0,0.2,0.4,0.6,0.8,1。质量分数,%)低合金钢,研究Mn含量对该合金组织与力学性能的影响。结果表明,合金组织由铁素体和珠光体构成。加入含Mn中间合金粉对混合原料粉末的压制性能没有明显影响。随Mn含量增加,合金中孔隙的数量增多,尺寸变大;合金密度先升高后降低,Mn含量为0.4%时合金密度最大,达到7.24 g/cm~3;合金硬度先升高后降低,Mn含量为0.6%时硬度最大;合金抗弯强度下降,冲击韧性升高,Mn含量超过0.4%时二者变化均较小。因此Fe-0.6Mn-1.4Cu-0.3C合金具有较好的综合性能,硬度(HRB)和冲击韧性分别达到57.4和8.80 J/cm~2,比Fe-2Cu-0.3C合金分别提高5.3和0.82 J/cm~2,材料呈部分韧性断裂特征。     

Age Hardening of the Al0.5CoCrNiTi0.5 High-Entropy Alloy

Al_0.5CoCrNiTi_0.5 high-entropy alloy was synthesized by vacuum arc melting in a copper mold. This alloy was aged at 773 K to 1473 K (500 °C to 1200 °C) for 24 hours to investigate the microstructure and hardness. The hardness of the as-cast alloy is HV743, and it exhibits a dendritic structure, in which dendrite is composed of body-centered cubic (bcc), face-centered cubic (fcc), and σ phases, and interdendrite is an eutectic structure consisting of bcc and order bcc phases. Apparent age hardening appears at 873 K to 1173 K (600 °C to 900 °C), and no age softening occurs even after 1473 K (1200 °C) aging. The age hardening of this alloy is attributed to the transformation of the bcc phase to σ phase. Detailed variations of hardness and the microstructure of aged alloys are reported in this article.     

Crystallization and characterization of substoichiometric compound (W0.5Al0.5)C0.5 obtained by solid-state reaction

(W_0.5Al_0.5)C_0.5 substoichiometric compound is synthesized by a combination of mechanical milling and high-pressure reactive sintering. X-ray diffraction is used to monitor the phase changes and crystallization of (W_0.5Al_0.5) C_0.5 during the whole reaction process. As a result, (W_0.5Al_0.5) C_0.5 is identified as the hexagonal WC-type belonging to the P-6m2 space group (No. 187), and the lattice parameters of (W_0.5Al_0.5)C_0.5 are calculated to be a=2.907 (1) Å, c=2.838 (1) Å, which are very similar to those of WC even if there are approximately 50 pct carbon vacancies in the cell of (W_0.5Al_0.5)C_0.5 as compared with WC. The substoichiometric (W_0.5Al_0.5)C_0.5 compound has a Vickers microhardness of 2385±70 kg mm^?2, which is as high as that of WC, while its density is far lower than that of WC.     

Substituting Effect of Y in La0.5Ba0.5 CoO3

La0.5-xYxBa0.5CoO3 polycrystals were prepared by solid state reaction. The substituting effects of Y for La on the magnetic and transport properties of the materials were studied systematically. The results indicate that substitution of Y induces two effects. Firstly, the charge transfer from Y to 3d orbital of Co happens. This causes the molecular magnetic moment to decrease. Secondly, the antiferromagnetic exchange interaction of Co ions appears. When the content of Y is less than or equal to 30%, the non-colinear structure of spins in materials is observed. When the content of Y is greater than 30%, the materials transit from predominant ferromagnetic state to predominant antiferromagnetic one. The conductive mechanism for the materials with different content of Y belongs to the variable range hopping conduction of polarons.The resistivity of materials increases sharply with increasing Y content.     

Magnetic and Transport Properties of La0.5-x Ndx Ba0.5 CoO3 Compounds

Substituting effects of Nd for La in La0.5Ba0.5CoO3 compounds were studied systematically. The results show that Nd doping does not change the itinerant properties of the Co3d electrons. The molecular magnetic moment of the mate-rials decreases monotonically with increasing Nd dopant. When Nd content x ≥0.45, a magnetic phase separation appears in the materials. When x ≤0.45, the Curie temperature decreases monotonically with increasing Nd dopant. This is due to the size effects of the rare earth ions. The electric resistance measurements show that in the studied temperature range, the conduction of the materials belongs to the thermo-diffusion conduction below the Curie temperature, while it belongs to the variable range hopping conduction of polarons over the Curie temperature.