304不锈钢注射成形用催化脱脂型喂料制备及其应用研究

以聚甲醛为粘结剂主要组元制备了催化脱脂型304不锈钢注射成形喂料,分析了喂料的热重性质、催化脱脂过程以及线收缩率,检测了烧结坯性能。结果表明:合适的注射温度应为180~200℃,脱脂温度在250℃以下;注射坯的平均密度为5.399 g/cm~3,烧结坯平均密度为7.829 g/cm~3;在长、宽、高方向上的线收缩率分别为:14.11%、14.02%和14.21%;烧结坯金相组织为典型奥氏体组织。     

304L不锈钢粉末注射成形研究

选用组分为POM、HDPE、PP以及其他辅助添加剂的粘结剂,与304L不锈钢粉末混炼制备注射成形喂料,研究了喂料,脱脂坯,烧结产品的性能。结果表明:粘结剂成分为85POM+8HDPE+7(PP+DBP)的喂料注射成形性最好,注射坯强度较高,催化脱脂效果好,脱脂过程中无明显缺陷,脱脂后坯体保形能力好。催化脱脂坯经过负压脱脂、真空内烧和强制冷却三个阶段的烧结后,产品密度为7.841 g/cm3,致密度为98.9%,硬度190 HV,抗拉强度550 MPa。     

磁控管用钼端帽的注射成形工艺

将HL MIM1钼粉与石蜡-高分子体系粘结剂混合成金属注射成形(MIM)喂料,制备钼端帽。喂料循环使用8遍,研究最大注射压力、进料量和生坯质量的波动,并研究其烧结性能。结果表明:该钼粉喂料具有较高的临界装载量(57%,体积分数)和注射流变特性。粘结剂在多遍重复使用中稳定性好,没有明显的降解行为,注射坯的质量波动可控制在±1.5%以内。烧结后钼端帽的晶粒尺寸小于10μm,密度为10.05 g/cm3,高于用美国及德国的商用MIM钼粉制备的钼端帽。端帽的纯度高于99.95%,C和O含量分别为8×10-6和10×10-6。密度和纯度均满足产品使用要求,且工艺稳定性好,已实现工业化生产。     

W-Ni-Cu高比重合金注射成形烧结收缩及性能的研究

研究了W-Ni-Cu高比重合金注射成形工艺过程收缩率和性能。比较了模具尺寸、注射坯尺寸、烧结坯尺寸，及烧结阶段各方向收缩率的关系，发现实际收缩与理论预测收缩率较为一致，但在厚度方向存在与其他方向收缩不一致的情形，这与由重力作用产生的塑料流动有关；还探讨了烧结坯密度与烧结条件的关系，测定了烧结坯的力学性能及断口形貌、金相组织，烧结坯在1400℃，90min烧结达到了99％的相对密度，断裂强度600MPa以上。     

金属粉末注射成形喂料在振动力场下的流变行为

脉动压力诱导金属注射成形技术将振动力场引入到金属粉末注射成形全过程中,振动力场对金属粉末喂料熔体的流变行为产生影响,从而提高注射型坯的质量。本研究采用毛细管脉动流变仪对石蜡-油-聚丙烯粘结剂体系的316L不锈钢粉末喂料动态流变行为进行测量和表征,并分析了振动频率和振幅对喂料的平均动态表观黏度的影响。结果表明振动力场的引入能改善喂料的流动性能,与相应的稳态条件相比,喂料的表观黏度显著下降。     

粉末注射成形中注射工艺参数对注射坯尺寸和密度的影响

通过单因子试验法研究了注射成形中注射温度、注射压力、体积流率、保压压力对注射坯尺寸和密度的影响,发现注射工艺参数的变化对注射坯的尺寸收缩、密度变化的影响很大且具有规律性;其中,注射温度和注射压力是对注射坯各项性能影响最大的参数。注射坯尺寸的变化对产品最终尺寸影响很小,可以忽略;而注射坯密度的变化对烧结后的尺寸精度影响很大。因此,在生产中要注意通过控制注射工艺参数来控制注射坯的密度以提高产品的尺寸精度。     

钨电极的金属注射成形工艺研究

以W-1.5%La2O3合金粉末为原料,采用金属注射成形技术,通过粉末和喂料的制备、注射、脱脂和烧结等工序,制造了一种薄壁、大长径比的杯状电极材料。研究了不同粒度的钨粉对于喂料制备和烧结工艺的影响,以及采用传统的烧结工艺和Ni元素活化烧结工艺对烧结坯的密度的影响。采用亚微米钨粉或活化烧结得到的镧钨电极的致密度达到98.3%,可以满足使用要求。     

金属注射成形蜡基粘结剂蜡含量对成形性的影响

采用不同石蜡含量的多聚合物组元粘结剂，研究石蜡含量对喂料粘度、生坯密度均匀性、和坯强度的影响。结果表明，石蜡含量的提高改善了喂料的均匀流变性能，但降低生坯的抗破坏能力。因此，可根据注射成形部件来选择适宜的蜡基粘结剂。     

粉末装载量对WC-10Co注射成形工艺影响的研究

采用差示扫描量热仪(DSC)、扫描电镜(SEM)、抗弯试验机(TRS)及维氏硬度计(HV)对不同粉末装载量(Φ=49%,53%,57%和61%(体积分数,下同))的WC-10Co注射成形过程中的喂料流变性、注射坯质量、溶剂脱脂速率和合金性能进行了观察和分析。结果表明:粉末装载量按4%逐步提高,包裹粉末和填充粉末颗粒间隙的粘结剂含量降低,聚合物组分熔融热敏感度降低、分解热敏感度提高,其喂料初始注射温度提高5～10℃,喂料流变性降低。粉末装载量从49%提高到61%,丝状粘结剂数量减少,粉末与粘结剂间的作用力和喂料颗粒间的联结作用降低,注射坯抗弯强度降低21.87%,注射坯质量降低。粉末装载量提高,溶剂脱脂机制相同,脱脂初始阶段以扩散为主,初始脱脂速率呈线性降低,相同脱脂时间(0～300 min)内粘结剂总脱除率降低。粉末装载量提高,合金的相对致密度和抗弯强度降低,Φ=61%时,WC-10Co合金的致密度、抗弯强度和硬度明显降低。     

纳米晶W-Ni-Fe粉的流变行为和烧结特性

研究了W-Ni-Fe纳米晶粉在注射成形中喂料的流变行为,纳米晶W-Ni-Fe粉采用机械合金化(MA)的方法制备,并将此粉末与蜡基粘结剂混合以形成一种喂料,讨论了MA球磨时间,纳米晶粉末体积和温度对喂料流变性的影响,随球磨时间增加,喂料的粘度以及粘度对剪切速率的敏感性降低,因此,在较长的球磨时间下,这种粉末喂料的流动性和成形性变好,随粉末体积增加,喂料的粘度遵循公式呈非线性增加,此时n=0.68.MA粉末喂料的粘度随温度和剪切速率的变化较小,所以注射温度和注射速度的变化对这种MIM注射坯的质量影响较小,本文也讨论了采用MA制备的W-Ni-Fe纳米粉末的烧结特性,实验结果表明球磨可以导致在液相烧结温度以下合金达到很高的密度,大的晶格畸变、晶粒细化和超饱和固溶体的形成,强化了烧结工艺。     

The role of pore evolution during supersolidus liquid phase sintering of prealloyed brass powder

ABSTRACT

The aim of this research is to study the pore structure as well as to assess the liquid phase sintering behaviour of Cu-28Zn powder specimens at different green density levels and temperatures. For this purpose, samples were compacted to obtain six different green densities and then sintered at 870°C, 890°C and in part at 930°C for 30?min. The results revealed that the spherical pores which are formed inside the grains can be swept by grain boundaries due to grain growth and join to primary pores so that secondary intragranular pores are eliminated and intergranular pores enlarged at higher temperatures. Also, the pores move upwards to the top of sample due to buoyancy forces. The role of pore structure in distortion is more tangible at higher temperatures (930°C) so that O-shape and X-shape distortions were observed at high and low green density samples, respectively.     

选择性激光熔化制备纯钨块体材料的研究

采用选择性激光熔化技术制备了纯钨块状样品, 研究了激光参数对所制备样品的表面形貌、内部晶粒组织和密度的影响。结果表明, 随着激光能量密度的增加, 样品表面变得光滑, 样品内部孔隙减少, 密度提高。采用功率300 W、扫描速率200 mm?s-1的激光扫描参数制备出了相对密度为97%的纯钨块状样品; 当激光功率提高至350 W时, 由于裂纹增多使样品密度下降; 随着激光输入能量密度的增加, 选择性激光熔化制备的样品内部晶粒方向性变得明显, 且晶粒尺寸增大; 采用扫描策略2 (激光功率200 W, 激光扫描速度200 mm?s-1)进行制备的样品内部孔隙较多, 且孔隙大多沿样品增材制造高度方向呈一条直线分布, 样品内部部分晶粒沿样品增材制造高度方向伸长。     

电渣炉大电流导体的电磁场数值模拟

 采用数值模拟的方法研究了电渣炉重熔期大电流导体产生磁场的空间分布规律。利用ANSYS软件包,通过求解磁矢量微分方程,确定了磁感应强度在空间的分布,计算结果与实际测量数据进行了对比。在自耗电极轴向方向上各点的磁感应强度在两端处大并且变化较大,中间磁感应强度最小;磁感应强度的总体趋势是随距离的增加而减弱,但在涡流区域将发生畸变,铁磁体表面的场强随深度增加而降低;在主回路中,各区域磁感应强度由强到弱的顺序为导线区域、电极区域、立柱和横臂区域、结晶器区域。     

Improving Conductivity of Copper PM Parts by Pretreatment of Green Compact

Abstract

There is a maximum green density to which pure copper can be compacted and still exhibit no growth upon sintering. This limits the maximum density and thereby the maximum conductivity and strength that can be achieved with sintered copper bodies. The swelling of a part pressed above this critical compacting pressure is caused by premature closure of the outer pores of the compact, thus sealing off the egress of internally generated gases. In this study a number of carefully selected chemical compounds were added to the as-pressed compacts using two methods in an effort to find a way of keeping these outer pores temporarily open until all internal gases are eliminated. These pores are then sealed off in the later stages of sintering, resulting in a higher density body with improved electrical conductivity throughout. Two compounds proved to be most effective in accomplishing this without leaving a residue deleterious to conductivity. Two commercial copper powders were die pressed into thick discs and then impregnated with an aqueous salt solution, the preferred treatment. After a special sintering procedure, the best conductivity obtained in an 18 mm diameter × 10 mm thick disc using the most responsive powder and treatment was 93·9% IACS at the centre and 94·2% IACS at the surface. Untreated, the same powder showed a maximum centre conductivity of 89% IACS.     

烧结温度对高速压制制备弥散强化铜材料导电率的影响

弥散强化铜材料具有高强度和高导电性的特性,孔洞是影响导电率的重要因素.本文采用高速压制成形技术,对Al₂O₃质量分数为0.9%的弥散强化铜粉压制成形,研究了压制速度对生坯的影响.当压制速度为9.4 m·s-1时得到密度为8.46 g·cm-3的生坯.研究了烧结温度对烧结所得Al₂O₃弥散强化铜试样导电率的影响.当生坯密度相同时,烧结温度越高,所得试样的导电率也越高.断口与金相分析表明:烧结温度为950℃时,烧结不充分,颗粒边界以及孔洞多而明显,孔洞形状不规则;烧结温度为1080℃时,颗粒边界消失,孔洞圆化,韧窝出现,烧结坯的电导率为71.3%IACS.      

明火式常化炉150℃低温回火能力诊断试验

为考察明火式常化炉(设计回火温度250~650℃)的低温回火功能,采用炉内钢板黑匣子测温的方法对该常化炉150℃的回火能力进行了诊断。结果表明,低温状态下该常化炉炉膛内炉气温度分布不均匀,边部炉温高于中部,且波动较大,宽度方向炉温均匀性较差;试验板坯加热温度厚度方向温差控制在±2℃,长度方向温差控制在±5℃,沿宽度方向温差则达20~28℃,边部加热温度明显高于中部。     

PowderMet2009: prospects improving after automotive debacle

Abstract

A homogeneous powder and binder distribution in the green body in powder injection moulding (PIM) is important. In the present study, the mould filling model of PIM has been developed, based on the multiphase fluid theory, viscosity model of feedstock and powder-binder drag force model. The particle Reynolds number is influenced by the particle size and density, resulting in the different drag force between powder and binder. Furthermore, the varied velocity of binder and powder will be obtained with numerical calculation of the continuity equations, leading to the change of green body homogeneity. CFX was used to simulate the mould filling in PIM. The results showed that the homogeneity of green bodies was relative to the filling patterns, which varied with different powder densities. The powders were not suitable for PIM when the particle size was bigger than 20 μm, and the fine powders were beneficial to improve the homogeneity.     

Thermal shock behavior of a three-dimensional SiC/SiC composite

Thermal shock behavior of a three-dimensional (3-D) SiC/SiC composite was studied using the water-quenched method. Thermal shock damage of the composite was assessed by scanning electron microscopy characterization and residual three-point-bending strength. In the thermal shock process, the composite displayed the same bending mechanical behaviors as those of the original composite and retained 80 pct of the original strength in the longitudinal direction after being quenched from 1200°C to 25°C in water for 100 cycles. However, the composite displayed anisotropy in resistance to thermal shock damage. The observed microdamage processes were as follows: (1) formation of micropores and long crack, (2) transfer and growth of pores, (3) saturation of the dimension and the density of pores, and (4) accelerated growth of the long crack along the longitudinal direction. The critical thermal shock number for the composite was about 50. When thermal shock was less than 50 cycles, the residual flexural strength of the composite decreased with thermal shock cycles increasing. When the number was greater than 50, the strength of the composite did not decrease further.     

凝胶离心成形制备YG10硬质合金管

将凝胶离心成形工艺应用于YG10复合粉末的坯体成形,研究了固含量对YG10复合粉末浆料的流变性的影响,分析了凝胶离心成形过程中引发剂量和压力对聚合速率的影响,并研究了离心转速对坯体和烧结体性能的影响。结果表明:以油酸作分散剂,制备稳定且流动性好的浆料最佳固含量为50%(体积分数),引发剂的加入量为5mmol/L(相对于预混液的体积),凝胶离心成形过程中压力能够加速浆料的固化,采用自行设计的离心成型机,选择最佳转速4 000r/min,制备出的坯体密度高、无残留气孔,相对密度57%,强度28.3MPa。坯体经真空脱胶烧结1 420℃保温1h制备出YG10硬质合金管,烧结体收缩均匀无变形,组织结构完整无偏析。