正交试验优选TC4钛合金粉体放电等离子烧结工艺

通过正交试验方法研究了放电等离子烧结制备TC4钛合金烧结体工艺中温度、压力和保温时间对其相对密度、硬度和显微组织的影响规律,根据烧结体相对密度和硬度优化了烧结工艺参数。结果表明:温度是影响烧结体性能和显微组织的关键因素,压力和保温时间对其影响较小;随着烧结温度升高,烧结体的相对密度逐渐增大,硬度先增大后减小,晶粒逐渐由等轴状向片层状演变,晶粒尺寸变大;随着压力增大,烧结体的相对密度增大,硬度先增大后减小;随着保温时间延长,烧结体的相对密度和硬度均呈递增的趋势;最优的烧结条件为烧结温度850℃、烧结压力40 MPa、保温时间8min,此时烧结体的相对密度和硬度均较高,分别为99.09%和42.3HRC。     

烧结温度对电磁压制Ag-25.5Cu-27Sn钎料显微组织及性能的影响

以纯金属粉末为原料,利用电磁压制技术制备了Ag-25.5Cu-27Sn钎料,并在100~500℃保温30 min进行烧结,研究了烧结温度对钎料相对密度、物相组成、显微组织、熔化特性,以及对其钎焊铜接头微观形貌和抗拉强度的影响。结果表明:随烧结温度的升高,钎料的相对密度先降低后升高,400℃烧结钎料的相对密度高于未烧结钎料的,并生成了稳定的ε_1-Cu_3Sn和ε_2-Ag_3Sn相;烧结使钎料的熔化温度略有提高,400℃烧结钎料的熔化温度比250℃烧结的降低了约4℃;400℃烧结钎料钎焊铜接头焊缝中的气孔数明显较少、组织均匀细小,其抗拉强度比未烧结钎料钎焊铜接头的提高了16%。     

烧结条件对整体CBN烧结密实体的影响

通过以Al为粘接剂和CBN为原料的整体刀具材料在不同的烧结条件下的烧结,并对烧结体进行了密度、磨耗比测试和SEM电镜扫描的微观形貌分析,发现温度和压力对其性能有很大的影响。结果表明:在压力一定的情况下,存在一个最佳合成温度,烧结体的磨耗比达到最大值。     

烧结工艺对拉丝模烧结区表面性能的影响

使用感应加热烧结方法,调整不同的工艺参数(温度、烧结次数)将金刚石料坯通过烧结粉烧结到不锈钢外套上,研究了烧结工艺参数对于金刚石拉丝模坯烧结区表面性能的影响。测量了各试样的显微硬度,并通过对试样进行显微形貌观察,分析了模坯试样出现显微硬度差异的原因。结果表明:烧结区域维氏硬度等均随着烧结温度的提高先增加后降低,在烧结温度为730℃时达到最大;烧结温度过低,烧结区存在气孔,而烧结温度过高,烧结区存在缩孔。经过预烧结工艺处理的PCD拉丝模坯,烧结区的表面质量和维氏硬度显著提高。     

还原再氧化工艺烧结温度对PTCR热敏材料性能的影响

针对片式正温度系数热敏电阻(PTCR)传感器的还原再氧化制备工艺,研究了还原性气氛下烧结温度对热敏材料性能的影响.结果表明烧结温度在1 215～1 295℃范围内的还原气氛下烧结,瓷体均可半导化,瓷体的平均晶粒尺寸随烧结温度升高而增大,增大趋势由缓慢到逐步加快.再氧化处理前瓷体电阻率均小于10 Ω·cm.再氧化后,瓷体的电阻率和升阻比都呈现出了不同程度的增长,增长幅度随烧结温度的升高而降低.此外,提高再氧化温度可提高升阻比同时会使瓷体电阻率增大.     

橡胶模成型和真空烧结制备碳化硼锆合金

以碳化硼、氢化锆-2粉为原料,用橡胶模成型和真空烧结的方法制备了碳化硼锆合金,用浸渍法测定烧结体的相对密度与开孔率,用扫描电镜分析了烧结体的微观结构,研究了碳化硼含量、成型压力、烧结温度、保温时间、助烧剂加入量对碳化硼锆合金相对密度的影响。结果表明:碳化硼对烧结有阻碍作用,烧结体的相对密度随碳化硼含量的增加而降低;坯体的成型压力越高,烧结温度越高,保温时间越长,烧结体的相对密度越高;锡粉有较好的助烧作用,但锡粉的质量分数不宜超过0.5%,如果添加量过高,烧结体的相对密度反而下降。     

工业生产条件下烧结温度对粉末冶金Fe-Cu-C合金组织和性能的影响

在实际工业生产条件下采用粉末冶金技术制备Fe-Cu-C合金,研究了烧结温度(1 060～1 160℃)对其密度、显微组织、物相组成、力学性能的影响。结果表明:随着烧结温度的升高,合金的密度先增大后降低,并在1 140℃时达到最大值(7.02 g·cm-3);随着烧结温度的升高,合金组织中颗粒的球化程度提高,孔隙的尺寸减小、数量降低,显微组织趋于稳定,铜相衍射峰消失,Fe4Cu3相衍射峰出现;合金的抗拉强度、硬度随烧结温度的变化趋势与密度的基本相同,且均在1 140℃时达到最大值,分别为460 MPa,185 HRB,拉伸断口均主要呈脆性断裂特征;工业生产条件下制备的合金的力学性能指标基本与在实验室条件下制备的相吻合。     

烧结温度对铜基粉末冶金摩擦材料组织和性能的影响

在不同烧结温度下(850~1 000℃)制备了铜基粉末冶金摩擦材料,研究了烧结温度对其组织、密度、硬度、抗压强度和摩擦磨损性能的影响,由此得到了最佳的烧结温度。结果表明:在不同烧结温度下,材料中的各组元均分布均匀,鳞片状石墨垂直于压制方向,并呈层状分布,SiO2以黑色大颗粒状镶嵌于铜基体内;随着烧结温度升高,孔隙的数量减少,尺寸减小,材料的硬度逐渐增大,密度和抗拉压度均先增大后减小,磨损量先降低后升高,磨擦因数逐渐降低;最佳的烧结温度为950℃,此时材料的密度为5.84g·cm-3,抗压强度为115MPa,摩擦因数为0.46,磨损量为0.063g。     

烧结温度对粉末冶金低合金钢显微组织和力学性能的影响

采用行程限制法将1300WB低合金钢粉压制成型并在不同温度下烧结制备了低合金钢,研究了烧结温度对其显微组织、微观形貌、密度、压溃强度和硬度的影响。结果表明:随着烧结温度升高,试样中孔隙的数量减少、尺寸减小,孔隙由连通状变得独立封闭,且孔形状由不规则形向球形转变;较低温度烧结试样的显微组织由珠光体、铁素体和渗碳体组成,随烧结温度升高,珠光体数量增多,试样的显微组织变均匀;试样的密度、压溃强度和硬度均随烧结温度升高而增大。     

硬质合金真空烧结和低压烧结的研究

分别在真空和低压下烧结制备混晶、细晶、高钴、高钛四类硬质合金,采用光学金相显微镜、洛氏硬度计、钴磁检测仪、矫顽磁力检测仪和抗弯强度检测仪等,对比研究了低压烧结和真空烧结的硬质合金的显微组织和性能。结果表明:对于混晶、细晶、高钴和高钛合金来说,和真空烧结相比,低压烧结均能降低合金的孔隙度,形成更均匀的组织,同时提高合金的密度和综合性能;低压烧结对合金组织和性能的影响程度和合金的成分有关,对于混晶和高钛合金来说,低压烧结对综合性能的提高较明显;而对于细晶和高钴合金来说,提高效果不明显。     

尼龙6／铜复合粉末选区激光烧结工艺参数优化及力学性能研究

制备了不同铜粉含量（质量分数）的尼龙6机械混合复合粉末,对复合粉末进行激光烧结,利用扫描电镜对烧结件的形貌进行了表征,通过正交试验优化工艺参数,并研究了铜粉含量对烧结件力学性能的影响。结果表明,铜粉与尼龙表面黏结良好,铜粉均匀分布在尼龙基体中;随着铜粉含量增加,烧结件抗弯强度、抗拉强度显著提高,冲击强度逐渐降低;铜粉含量为50％时,烧结试样抗拉强度为43．28MPa,抗弯强度为77．66MPa,硬度为112HRL,分别比纯尼龙6提高了10．04％、59．27％和39．29％。     

PA6粉末选区激光烧结多层应力分析

选区激光烧结成型过程中,激光束扫描时反复的加热、冷却带来不均匀的热应力,影响烧结过程和烧结件的质量。基于弹性变形原理,利用单轴应力作用下的变形梁的挠曲和应变与应力之间的关系,来分析烧结过程中的应力以及不同烧结层之间的相互影响,结果表明,在每个单层烧结时,烧结应力主要集中在烧结层的上表面和下表面的两端,且呈现为拉应力;在多层烧结时,烧结的热载荷对紧邻已熔接层的应力有直接影响,随着烧结层数增加,新烧结层对已熔接层的热影响逐渐减小,对应的随着温度变化较小,已熔接层的应力也较小且保持较低水平。     

抗震底座树脂模具强度研究

SLS技术处理后的烧结件用于模具时,为提高树脂模具的强度,对影响树脂模具强度的树脂混合液涂料质量、涂抹时间和涂抹后的固化处理工艺进行研究。试验表明,受树脂混合液涂料成分的影响,树脂混合液涂料应在45min内均匀涂抹在烧结件上;不同的烧结件所需要的树脂混合液涂料质量也有所不同;涂抹后的烧结件在常温下放置一段时间后再放入恒温干燥箱进行渐次升温固化处理可以明显提高树脂模具的强度。     

SLS预热温度场温度补偿研究

由于预热粉床的温度分布不均匀,很难获得强度、精度较高的烧结制件,针对以上问题,提出了通过温度补偿改善预热粉床的温度分布不均匀对激光烧结成型制件质量的影响,通过温度补偿调节粉床的温度分布,从而提高了烧结制件的质量,并对粉床温度场进行有限元模拟。研究结果表明,增加热源的方式对预热粉床进行温度补偿可以明显改善温度场;通过试验获得了温度补偿的最佳工艺组合。     

Powder injection molding 440C stainless steel

In this work, the processing steps for producing 440C stainless steel parts by means of powder injection molding technique were investigated. The molded specimens were debinded by solvent debinding followed by thermal debinding methods and were sintered under vacuum atmosphere. Effective densification took place in the temperature range 1,230–1,240°C in the sintering. After heat treatment, specimens sintered at 1,240°C for 30 min had the tensile strength of 876.3 MPa, the hardness of 57.7 HRC. Pitting mainly occurred in injection molding 440C stainless steel specimens in NaCl solution. The content of carbon has serious effect on the shape retention. Some methods, such as preventing from oxidation, are presented to avoid the as-sintered specimens from deformation.     

Tribological behaviour of sintered 316L stainless steel impregnated with MoS2 plain bearing

The mechanical and tribological properties of sintered 316L stainless steel impregnated with molybdenum disulfide (MoS₂) were investigated. Tests were carried out at room temperature for two specific ranges of PV value (1.1 and 1.8 MPa m/s). The results prove that the friction coefficient and the wear are strongly influenced by the addition level of MoS₂.

In this paper, MoS₂ powder was mixed with 316L powder before being processed via compacting and sintering steps. The microstructure, hardness, tensile strength and elongation at breaking point of the sintered specimens were evaluated. The friction and wear properties of the materials were examined by a partial plain bearing wear test rig under dry conditions at room temperature and in air. Although some of mechanical properties of the composite decreased with increasing MoS₂ amount, the MoS₂ was very effective in reducing the friction and wear of the composites. Particularly, the sintered 316L–15% MoS₂ materials at 1.1 PV value showed a reduction of friction coefficient by approximately 20–25% when compared to the sintered 316L specimen without addition of MoS₂. In addition, wear of specimen with addition of MoS₂ was also reduced to some extent (5–10% weight loss reduction) at this specific PV value.     

氮化碳基陶瓷刀具材料的制备与力学性能研究

采用热压烧结工艺,以Ti(C, N)为添加相,以Mo、Ni和Co为金属相,成功制备了氮化碳(C₃N₄)基陶瓷刀具材料,测量了其断裂韧度、抗弯强度和维氏硬度,分析了其微观组织。结果表明,在烧结温度为1600℃、保温时间为45 min和烧结压力为32 MPa的工艺条件下,Ti(C, N)质量分数为35%、Ni-Co质量分数为8%的C₃N₄基陶瓷刀具材料力学性能最优。合适的Ti(C, N)含量能细化C₃N₄晶粒、提高烧结密度、改善力学性能,合适的Ni-Co含量能使微观组织细小均匀。     

Scan pattern, stress and mechanical strength of laser directly sintered ceramics

A finite element model was developed to simulate the influence of laser scan patterns (laser jump patterns, ratio of length to width and laser scan angle) on the temperature and stress distributions in the process of laser direct sintering ceramics. The effects of laser scan patterns on the stresses in the laser directly sintered ceramic samples were investigated by simulation. Different ceramic samples were prepared by the laser sintering process for the four-point bending strength measurement. The simulation results consist with the experimental ones. The results in the present research can be used to optimize process route for the laser direct sintering process and provide a guidance for selecting the laser processes parameters for high mechanical strength ceramic components.     

Microstructural and mechanical properties of nanometric magnesium oxide particulate-reinforced aluminum matrix composites produced by powder metallurgy method

In this research, aluminum alloy (A356.1) matrix composites reinforced with 1.5, 2.5 and 5 Vol.% nanoscale MgO particles were fabricated via powder metallurgy method. Pure atomized aluminum powder with an average particle size of 1μm and MgO particulate with an average particle size between 60 to 80 nm were used. The specimens were pressed by Cold Isostatic Press machine (CIP), and were subsequently sintered at various sintering temperatures, viz. 575, 600 and 625°C. Optimum amount of reinforcement and sintering temperature were determined by evaluating the density, microstructure and mechanical properties of composites. The composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Hardness and compression tests were carried out in order to identify mechanical properties. Reinforcing the Al matrix alloy with MgO particles improved the hardness and compressive strength of the alloy to a maximum value of 44 BHN and 288 MPa, respectively. The most improved compressive strength was obtained with the specimen including 2.5% of MgO sintered at 625°C. According to the experiments, a sintering temperature of 625°C showed better results than other temperatures. A good distribution of the dispersed MgO particulates in the matrix alloy was achieved.