Shape memory TiNi powders produced by plasma rotating electrode process for additive manufacturing

This study aimed to produce spherical TiNi powders suitable for additive manufacturing by plasma rotating electrode process(PREP).Scanning electron microscopy,X-ray diffractometry and differential scanning calorimetry were used to investigate the surface and inner micro-morphology,phase constituent and martensitic transformation temperature of the surface and inner of the atomized TiNi powders with different particle sizes.The results show that the powder surface becomes smoother and the grain becomes finer gradually with decreasing particle size.All the powders exhibit a main B2-TiNi phase,while large powders with the particle size≥178μm contain additional minor Ti2Ni and Ni3Ti secondary phases.These secondary phases are a result of the eutectoid decomposition during cooling.Particles with different particle sizes have experienced different cooling rates during atomization.Various cooling rates cause different martensitic transformation temperatures and routes of the TiNi powders;in particular,the transformation temperature decreases with decreasing particle size.

Solidification Behavior and Microstructures Characteristics of Ti-48Al-3Nb-1.5Ta Powder Produced by Supreme-Speed Plasma Rotating Electrode Process

In this study,the characteristics and solidification behavior of Ti-48Al-3Nb-1.5Ta powder produced by supreme-speed plasma rotating electrode process(SS-PREP®)were investigated.The microstructure,phase and characteristics were analyzed by scanning electron microscopy,X-ray diffraction and other methods.The atomization mechanism is direct drop formation.The relationship between the particle size and cooling rate is vc=3.14×10^(-7)·d^(-2)+1.18×10^(-2)·d^(3/2),and the relationship between secondary dendrite arm space and the particle size isλ=0.028d+0.11,as well as the relationship between SDAS and cooling rate isλ=4.84×10^(-5)·T^(-1.43).With increase in particle size,the surface structure gradually changes from the featureless smooth structure to dendritic and cellular dendritic morphology,and the flow ability becomes better.The carbides mainly exist within 5 nm of the surface and the oxidation layer is about 20 nm thick.Ti-48Al-3Nb-1.5Ta powder was mainly composed ofα2 phase andγphase.With increase in particle size,the content ofγphase increases,and the hardness decreases accordingly.The 106–250μm particles are composed of multiple grains with the grain size of 70–80μm.The microstructure,phase composition and hardness of different TiAl powders with the same size are similar,but the elastic modulus is different.

PREP工艺参数对GH3536高温合金粉末性能的影响

采用等离子旋转电极雾化法(Plasma Rotating Electrode Process,PREP)制备GH3536合金粉末,探究电极棒旋转速度和电流强度对粉末粒度及其物性能的影响。结果表明,粉末平均粒径随着旋转速度的提高而减小,当旋转速度为16000 r·min^(-1)时,粉末的D50粒径最小为27μm。在棒料转速一定时,随着主弧电流强度的增加,粉末的平均直径逐渐增大,当电流强度由1300 A提高至1500 A时,粉末D50粒度从33μm增加至42μm。此外,棒料旋转速度和主弧电流的增加能够改善GH3536粉末的流动性与松装密度。经过综合考虑,旋转速度14000 r·min^(-1)、电流1300 A、进给速度0.8 mm·s^(-1)工艺的参数组合最为适宜。

Influence of Processing Parameters on Granularity Distribution of Superalloy Powders during PREP

In order to investigate the influence of processing parameters on the granularity distribution of superalloy powders during the atomization of plasma rotating electrode processing (PREP), in this paper FGH95 superalloy powders is prepared under different processing conditions by PREP and the influence of PREP processing parameters on the granularity distribution of FGH95 superalloy powders is discussed based on fractal geometry theory. The results show that with the increase of rotating velocity of the self-consuming electrode, the fractal dimension of the granularity distribution increases linearly, which results in the increase of the proportion of smaller powders. The change of interval between plasma gun and the self-consuming electrode has a little effect on the granularity distribution, also the fractal dimension of the granularity distribution changed a little correspondingly.

Numerical analysis on solidification process and heat transfer of FGH95 superalloy droplets during PREP

In order to understand the relation between microstructure of superalloypowders and its solidification progress, the processing parameters are optimized during plasmarotating electrode processing (PREP). It was predicted from the results that the droplet velocities,droplet temperature, and fractional solidification with flight time about FGH95 superalloy droplethave been carried out based on Newtonian heat transfer formulation coupled with the classicalheterogeneous nucleation and the specific solidification process. It has been found that the dropletdynamic and thermal behavior is strongly affected by the distribution of droplet diameters, theproportion of cooling atmosphere, but is relatively unaffected by the droplet superheat.

Analysis and control of inter-electrode gap during leveling process in counter-rotating electrochemical machining

The inter-electrode gap(IEG) is an essential parameter for the anode shaping process in electrochemical machining(ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM(CRECM)is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.

等离子旋转电极雾化熔滴的热量传输与凝固行为

建立了在等离子旋转电极雾化 (PREP)制取合金粉末的过程中雾化熔滴的轨道运动方程 ,讨论了雾化熔滴在凝固过程中的热量传输与凝固行为 ,并确定了定量计算换热系数所需的雾化熔滴初始速度。用数值求解方法计算了FGH95高温合金雾化熔滴在PREP过程中的速度及其在凝固过程中的温度、固相分数、冷却速率等凝固参数。结果表明 :在作者提出的工艺参数下 ,FGH95合金熔滴的冷却速率达 10 4 K/s量级以上 ,合金过热度对冷却速率的影响主要在全液态阶段 。

等离子旋转电极雾化FGH95高温合金原始粉末颗粒中碳化物的研究

利用扫描电镜 (SEM)和透射电镜 (TEM)对等离子旋转电极雾化 (PREP) FGH95高温合金原始粉末颗粒中的碳化物进行研究 ,并分析了 PREP FGH95合金原始粉末颗粒中碳化物在凝固过程中的形成机理 ,结果表明 :粉末颗粒内部中存在 MC′型碳化物及微量 L aves相和 M3B2 相 ,MC′型碳化物形态有块状、条状、花朵状 ,草书状 ,粉末颗粒的冷却速率以及已凝固基体在枝晶间所产生的内应力 ,是导致粉末颗粒中 MC′型碳化物形态多样。

用等离子旋转电极法制取镍基高温合金粉末

文章介绍了等离子旋转电极法制粉的装备、原理、工艺参数，以及所制取的镍基高温合金粉末的特性。

预热处理对FGH95高温合金粉末中碳化物的影响

对等离子旋转电极雾化(PREP)FGH95高温合金粉末颗粒在不同温度下进行预热处理,并对热处理粉末中碳化物的变化规律进行分析,结果表明:经预热处理,粉末颗粒中的MC’型亚稳碳化物发生分解和转变,析出稳定的MC,M_(23)C_6及M_6C型碳化物,明显改变碳化物的稳定性和分布状态。

雾化法制备高品质钛合金粉末技术研究

研究了惰性气体雾化法和等离子旋转电极法两种雾化法制备工艺所得TA15钛合金粉末的化学成分、粒度分布、颗粒形貌及微观组织。结果表明,雾化法制备的粉末间隙元素增量低,而且颗粒球形度高,颗粒内部是细小的胞状显微组织;惰性气体雾化法制备的粉末细粉收得率较高,有较多的吸附颗粒,颗粒内部有气孔;等离子旋转电极法制备的粉末粒度分布范围窄,颗粒呈规则的球形,表面光亮、圆滑。

低温复杂结构件特种成形工艺

研究了等离子旋转电极制备低温钛合金球形粉末的特性,采用热等静压成形工艺,制备低温钛合金粉末冶金材料,并对比分析了组织与性能。以低碳钢为材质,加工装配专用芯模,开展粉末冶金TA7ELI钛合金构件净成形技术研究,实现了大尺寸、薄壁、半封闭式火箭发动机低温转子高性能、高可靠性的整体净成形。结果表明:等离子旋转电极制备的低温钛合金球形粉末,具有非常高的球形度和振实密度,粒径分布可依据需求控制在一定范围内,非金属夹杂含量每千克不超过20个;粉末冶金低温钛合金材料性能全面达到同批次锻件性能水平,微观组织呈等轴状;粉末冶金低温钛合金氢泵叶轮已通过了发动机型号低温全程试车考核。

等离子旋转电极法所制取的镍基高温合金粉末中异常颗粒的研究

归纳了用等离子旋转电极法 (PREP)制造的镍基高温合金粉末成品粉中常见的异常粉末颗粒类型 ;

TA7 ELI粉末冶金材料力学性能与显微组织

以TA7 ELI钛合金棒为原料,用等离子旋转电极工艺制备出高品质钛合金球形粉末。采用热等静压成形工艺,将粉末压制成钛合金材料,并研究了材料的组织和力学性能。结果表明:等离子旋转电极工艺制备的钛合金球形粉末具有非常高的球形度和振实密度,粒度分布比较窄,非金属夹杂含量非常低;热等静压制备的低温钛合金达到全致密,其组织均匀细小,具有各向同性,性能达到锻件水平。

电渣重熔-等离子旋转电极雾化制备高品质316H奥氏体不锈钢粉末

首先采用电渣重熔法熔炼316H奥氏体不锈钢母合金,随后采用等离子旋转电极雾化(PREP)法制备了球形316H奥氏体不锈钢粉末。利用氧氮分析仪、扫描电镜(SEM)、X射线衍射仪(XRD)、霍尔流速计和激光粒度分布仪等研究了粉末的氧含量、形貌、相结构、流动性、松装密度、振实密度及粒度分布。结果表明:电渣重熔制备的316H奥氏体不锈钢母合金全氧含量为20×10^(-6),铸锭成分均匀;等离子旋转电极雾化法制备的316H奥氏体不锈钢粉末全氧含量为70×10^(-6),粉末粒度呈现双峰分布,细粉收得率高,粒径为15~150μm的粉末占比近80%,粉末粒径分布范围广、球形度高、卫星粉少。粉末表面基本为胞状晶,截面为均匀的枝晶组织,为单一的γ-Fe相结构。制备态粉末的霍尔流速、松装密度和振实密度分别为14.83 s·50^(-1)g^(-1)、4.725 g·cm^(-3)和5.401 g·cm^(-3)。粗粉和细粉质量分数各占一半时,粉末的霍尔流速为12.91 s·50^(-1)g^(-1),小于初始粉末的霍尔流速,提高了粉末的流动性能。长时间的真空储存能降低粉末的带电性能,进而降低粉末颗粒之间排斥作用,可进一步提高粉末流动性。粗、细粉之比为7:3时,粉末的填充性能最好,填充率高达70.6%。

ui3D打印用钛及钛合金粉末制备工艺的研究现状

3D打印技术是目前研究较多的一种快速成型技术,钛及钛合金由于具有优异的物理、化学和力学性能,使其在多个领域广泛应用,钛及钛合金粉末是3D打印重要的原料。本文介绍了制备钛及钛合金粉末的方法,包括惰性气体雾化法、等离子旋转电极法和射频等离子体法,简单阐明了各种制备方法的原理、应用以及国内外的研究进展。

等离子旋转电极雾化熔滴凝固过程的数值计算

在Newton冷却模型的基础上,用数值求解方法计算了FGH95高温合金在等离子旋转电极雾化(PREP)过程中雾化熔滴的温度、固相分数、冷却速率等凝固参量随工艺参数的变化规律。结果表明:合金过热度对凝固参量的影响主要在全液态阶段,电极棒转速大小对熔滴凝固过程有一定影响,而雾化熔滴的冷却速率及固相分数等对氩氦气体的混合比例极为敏感。

等离子旋转电极法制备3D打印用GH3536高温合金球形粉末

本文选用等离子旋转电极法制备了GH3536高温合金粉末,研究了电极棒的转速,等离子弧电流强度对粉末性能的影响。结果表明,粉末的粒度随转速的提高而减小,粒度主要集中在25~100μm,,通过扫描电子显微镜发现,粉末基本呈现球形,球形度可达到93%以上,可能满足3D打印的要求。

高转速PREP法制备钛合金粉末工艺研究

采用高转速PREP法制备TC4钛合金粉末;并将其用于SLM成型。利用扫描电子显微镜、全自动粒度粒形分析仪及氧氮分析仪对粉末形貌、粒度粒形及氧氮含量进行测量;分析讨论制备工艺对粉末形貌、粒度、球形度、合金元素含量和收率的影响。利用金相显微镜、万能电子试验机研究SLM工艺及粉末性能对TC4钛合金组织性能的影响。结果表明,电极转速越高,粉末粒径越小、球形度及细粉收率越高;采用50000r·min^(-1)转速可制得形度96.8%、细粉收率14.3%的TC4钛合金粉末。TC4钛合金粉末具有龟裂表面和光滑表面两种形貌;粉末粒径越小表面越光滑、球形度越高、Al和V元素含量越高。采用SLM成型工艺制得的TC4钛合金的拉伸及屈服强度均可达1200MPa以上,弹性模量达到120GPa以上。

等离子体旋转自耗电极端部熔池中的流场分析

运用Ｎｅｗｔｏｎ流体力学的微元法分析，通过对等离子体旋自旋自耗电极（ＰＲＥＰ）端部小熔池中液膜流动的稳态层流假设，建立了液膜中流体运动的微分方程．并运用相关边界条件，得到了该微分方程的解析解，由此得到液膜厚度的表达式．该式表明液膜厚度与等离子体电弧功率、ＰＲＥＰ直径及旋转速度存在依赖关系．通过改变这些工艺参数，进行了实验验证，结果表明，实测的液膜厚度同理论计算值符合较好。