复合电冶熔铸WC颗粒增强钢基复合材料的显微缺陷研究

采用复合电冶熔铸工艺制备了WC颗粒增强钢基复合材料,该工艺具有高能球磨混粉均匀、电渣重熔精炼净化、电磁搅拌颗粒分散、水冷结晶逐层快速凝固等特点,熔炼过程中有利于气体排出、夹杂物的去除、WC颗粒的分散等,较好地解决了颗粒团聚和聚集问题.得益于较快的冷却速度,WC颗粒被钢液吞没,尽可能地避免了枝晶偏析,使晶粒得到细化.所制备的复合材料孔隙少、致密高、无夹杂,WC颗粒分布均匀,缺陷很少.

铜包Q195钢复合线材的组织与性能

采用复合熔铸-旋煅法制备了铜包Q195钢复合线材,通过拉伸试验、组织观察、电阻率测试等对其力学性能、组织形貌及电学性能进行了研究。结果表明:熔铸后铜和钢的结合面呈锯齿状,界面较清晰,组织较为粗大,无中间相形成,旋锻后组织细小;直径为2,3.4,4 mm的钢芯制备的铜包钢复合棒材旋锻后制得的复合线材的抗拉强度分别是260.63,368.83,419.12 MPa,电阻率分别为1.981×10^(-6),1.976×10^(-6),2.035×10^(-6)Ω·cm;旋锻后横截面上钢芯的面积比越大,其抗拉强度越接近纯钢芯的;铜包钢复合线材拉伸断口出现大量韧窝,断裂方式为典型的韧性断裂。

热处理对复合电冶熔铸WC颗粒增强钢基复合材料力学性能的影响

采用复合电冶熔铸工艺制备了以5CrNiMo钢为基体、WC颗粒为增强相的颗粒增强钢基复合材料,通过宏微观硬度试验、三点弯曲试验和冲击韧性试验对比分析并综合评定复合材料和5CrNiMo钢的各项力学性能,同时采用扫描电子显微镜观察断口形貌并判定断裂机理。结果表明：大量WC颗粒增强体分布在较软的钢基体上,提高了复合材料的整体硬度,淬透性和淬硬性也较好,但塑性比5CrNiMo钢稍差。在950℃到1050℃淬火时,复合材料的洛氏硬度达到60-66 HRC,抗弯强度达到1600-1650 MPa,均呈现先上升后下降的波动趋势,而冲击韧度变化不明显。对比基体和中小块WC颗粒聚集区,大块硬质相的显微硬度值变化幅度较小。在锻造退火状态下,复合材料为准解理＋韧窝的复合断裂机理,而在淬火回火态时,则转变为解理断裂机制。

电冶熔铸WC颗粒增强钢基复合材料的干滑动摩擦磨损性能

通过调整WC颗粒尺寸(50μm和100μm)和质量分数(25%、35%和45%),采用新型的复合电冶熔铸工艺制备了4种WC颗粒增强钢基复合材料,以及作为对比的5Cr Ni Mo钢,对经过不同热处理的复合材料进行干滑动摩擦磨损试验,研究了各试样的摩擦因数和磨损量,并对磨损形貌进行分析。结果表明:随着WC含量或颗粒度在一定范围内增大,摩擦因数呈提高的趋势。在1000℃淬火+180℃回火,粗颗粒的WC含量为45%时,复合材料表现出最佳的耐磨性,是5Cr Ni Mo钢的21.96倍,是粗颗粒含量25%和35%时的10.65倍和8.91倍,是细颗粒含量45%时的5.35倍。PRMMC在干滑动摩擦磨损条件下的磨损机制为磨粒磨损和氧化磨损。

三种不同材质磨煤机的辊套和衬板使用情况

介绍了在ZGM113G-Ⅰ型中速磨煤机上先后使用过的三种不同材质的辊套和衬板,分析了辊套和衬板的化学成分及铸造工艺特点,对比了辊套和衬板的磨损速率、使用寿命以及磨损形状对磨煤机性能的影响。结果显示,高铬堆焊产品略优于高铬铸造产品,复合熔铸金属陶瓷产品远优于前两种产品,使用寿命可达16 070h,同时,大幅延长了检修周期,增加了磨煤机出力,降低了单位电耗,性价比高。

Effect of complex melt-refining treatment on microstructure and mechanical properties of sand-cast Mg–10Gd–3Y–0.5Zr alloy

The effect of complex melt-refining treatment （melt flux incorporating with rotating gas bubble stirring） on microstructure and mechanical behavior of the sand-cast Mg-10Gd-3Y-0.5Zr alloy was investigated. In addition, the melt purifying mechanism of the complex melt-refining treatment for the sand-cast alloy was discussed systematically. The results show that the new melt-refining method can significantly improve melt quality and mechanical behavior of the tested alloy, i.e., compared to the reference unpttdfied alloy, the volume fraction of inclusions decreased from 0.47% to 0.28%, the ultimate tensile strength and elongation for T6-treated alloy increased from 245 MPa and 0.7% to 312 MPa and 4.5%, respectively. Especially, combining 1% flux with rotating gas bubble stirring can get even better purifying effectiveness than conventional sole 2% flux purification; the use of melt flux decreased by 50% and significantly reduced environmental pollution.

Infiltration of A6063 aluminium alloy into SiC-B_4C hybrid preforms using vacuum assisted block mould investment casting technique

Production of A6063/SiC-B4C hybrid composite using vacuum assisted block mould investment casting was investigated. Firstly,SiC-B4C hybrid preforms were fabricated in cylindrical shape.The preferred mean particle size of the SiC and B4C powders were 60μm and 55μm respectively.In early experiments,single powder ratio of 85%SiC and 15%B4C was selected to produce the tough preforms.Subsequently,the preforms were placed into the cylindrical shape gypsum bonded block investment moulds and A6063 alloy was infiltrated into the preforms using vacuum assisted（-10 5 Pa）casting machine.Porosity fraction of preforms was determined using Archimedes’test.The fabricated cast specimens were characterized using hardness tests,image analysis and SEM observations and EDX analysis.The result indicates that,by the vacuum assisted block mould investment casting technique,the infiltration of the preforms by molten metal was successfully realized.

Microstructure and mechanical properties of ADC12 composites reinforced with graphene nanoplates prepared by ultrasonic assisted casting

Microstructure and mechanical properties of ADC12 composites reinforced with graphene nanoplates(GNPs)prepared by high-intensity ultrasonic assisted casting were investigated.The results indicated that high-intensity ultrasound can promote the uniform distribution of GNPs in the melt,resulting in refining theα(Al)phase and Si phase.The optimal addition of GNPs was 0.9 wt.%,and the optimal ultrasonic time was 12 min.The tensile strength,the yield strength and the hardness of the composite produced under the optimal parameters were 256.8 MPa,210.6 MPa and HV 126.0,respectively,which increased by 30.5%,42.7%,and 34.8%compared with those of the matrix,respectively.After adding the GNPs,the fracture mechanism gradually turned from a brittle fracture to a ductile fracture.The good interface and distribution allowed GNPs to play the role in fine grain strengthening,dislocation strengthening and load transfer strengthening effectively.