机械球磨对Ti-Al复合粉扩散反应的影响

研究了粉末烧结制取Ti-Al金属间化合物过程中,机械球磨对Ti、Al混合粉扩散反应的影响.结果表明,机械球磨使Ti、Al混合粉形成具有层片结构的复合粉,且球磨时间越长,层片越薄越均匀.在固相下对不同球磨时间的Ti、Al混合粉压坯试样进行烧结后,通过X射线衍射、扫描电镜及能谱分析,结果表明,球磨时间越长,越有利于Ti、Al之间的扩散反应,越容易形成Ti-Al金属间化合物,并有利于组织的均匀化.     

机械球磨对Ti/Al混合粉末组织和热稳定性影响的研究

为了探索一种制备高综合性能TiAl基金属间化合物的新方法，研究了机械球磨对Ti、Al粉末微观组织及其热稳定性的影响，结果表明，在机械球磨的作用下Al粉末晶粒以高于Ti的速率细化，最终形成局部含少量Ti 纳米晶的非晶，但在整个过程中未发现Ti、Al元素相互扩散形成Ti-Al金属间化合物中间相；不同球磨时间作用下的Ti/Al粉末中贮有不同的能量，且随时间的延长而增加，以非晶化粉末最为显著，内能的增加是由于机械合金化过程引入了大量的微观缺陷所致，对不同球磨时间的粉末进行热处理显示，球磨时间的增加可大幅度降低形成Ti-Al金属间化合物的温度，球磨75h的复合粉末甚至在350℃，保温1h即可转变成金属间化合物。     

Ｎi—Al喷涂层中温反应烧结的温度变化模型

基于Ｎi-Al喷涂层反应烧结的特点，提出了涂层反应放热过程的温度变化模型及计算方法，研究了Ni-Al混哈喷涂层（９４％Ｎi 6%Al）在中温保护气氛下反应烧结的界面组织及反应区温度变化过程，计算表明：反应区存在非金属间化合物液相，同时由于Ni-Al在中温条件下发生反9应并在局部形成高温，使涂层具有良好的力学性能。     

Ti-Al球磨粉反应等离子喷涂涂层的组织与性能

为制备Ti-Al金属间化合物复合涂层并研究其性能,以机械球磨的Ti-Al混合粉在Q235钢表面进行反应等离子喷涂实验,分别采用X射线衍射、扫描电子显微镜对涂层的成分、显微组织进行了分析,并测试了涂层的结合强度、显微硬度和耐腐蚀性能.结果表明:涂层由Al3Ti、TiN、Al2O3、少量TiAl与Ti3Al、以及残留的Al和Ti组成;球磨可促进喷涂时的反应,但喷涂时Al和Ti仍未完全反应,且在空气环境中喷涂容易氧化和氮化;涂层与基体之间是镶嵌式的机械结合,结合强度平均为30.24 MPa;涂层表面的显微硬度平均为206.1 HV,涂层的耐腐蚀性优于基体.总体上看,当球磨时间较长、电流较大、喷涂距离较大、气流量较小时,喷涂时的反应较充分,且涂层比较均匀、致密,其强度、硬度以及耐腐蚀性能较高.     

粉末烧结形成Al基金属间化合物的研究

采用粉末烧结方法,利用光学显微镜、扫描电子显微镜和X射线衍射技术研究了二元Co/Al和Mn/Al混合粉末的扩散反应,并依据TFDC电子理论对实验结果进行了讨论.结果表明:对于Al-Co体系,Al原子向Co扩散,扩散的前锋在靠近Co的一端,在粉末颗粒界面处形成了CoAl,Co2Al5金属间化合物,这些化合物中CoAl数量最多,该化合物的成分离Co最近;对于Al-Mn体系,Mn原子向Al扩散,扩散的前锋在靠近Al的一端,在粉末颗粒界面处形成了Mn5Al8,Mn22Al78,MnAl6金属间化合物,这些化合物中MnAl6数量最多,成分最接近Al.     

机械球磨与包套挤压制备Al-Pb合金

采用机械球磨(MM)制备了Al-20(Wt.%)Pb复合粉,通过X射线衍射和电子探针分析了Al20Pb复合粉及其层片状组织.为得出最佳球磨工艺参数,对复合粉进行了压制和烧结实验.结果表明:球磨6 h得到的Al-20Pb复合粉具有均匀细小的层片结构,既保持较好的塑性,易于致密,又能在烧结后得到均匀细小的显微组织.     

铝合金／铜／不锈钢接触反应钎焊接头微观组织分析

采用接触反应钎焊对6063铝合金／镀铜层／1Cr18Ni9Ti不锈钢进行焊接,借助扫描电子显微镜和电子探针对接头的微观组织及Fe—Al国金属间化合物生长情况进行测试和分析。结果表明：钎缝中靠近不锈钢一侧为Fe—Al金属间化合物层,靠近铝合金一侧主要是Cu（Al）固溶体,中心区域由Cu-Al化合物和Cu（Al）固溶体混俞而成;随着保温时间的延长,化合物层厚度随之增加,Cu在铝合金一侧富集出现晶界渗透现象;钎缝中首先产生Cu—Al金属间化合物,之后共晶液相中的Al原于穿越Cu—Al金属间化合物层和残余镀铜层扩散至不锈钢侧,与Fe原子生成少量Fe—Al金属间化合物。     

机械合金化能量转换与Ni50Ti50非晶合金的形成

本文报道了球磨转速，装球量对Ｎｉ５０Ｔｉ５０单质混合粉机械合金化的影响，并建立模型用于计算工艺条件对球磨能量转换的影响，进而讨论了它与机械合金化相变反应方式的关系。粉末在每次碰撞的变形能过高时，可能形成金属间化合物，而粉末经长时间球磨获得的总能量超这一定值将引起非晶的晶化。     

机械合金化能量转换与Ni_(50)Ti_(50)非晶合金的形成

本文报道了球磨转速,装球量对 Ni_(50)Ti_(50)单质混合粉机械合金化的影响,并建立模型用于计算工艺条件对球磨能量转换的影响,进而讨论了它与机械合金化相变反应方式的关系。粉末在每次碰撞的变形能过高时,可能形成金属间化合物,而粉末经长时间球磨获得的总能量超过一定值将引起非晶的晶化。     

球磨时间对TiB_2-Ni(Al)复合粉末组织结构影响研究

在不同球磨时间条件下,采用机械球磨方法制备TiB_2-Ni(Al)复合粉末,其中Ni粉和Al粉的物质的量比为1∶1,TiB_2陶瓷相含量为40%(体积分数)。采用扫描电子显微镜(SEM)以及X射线衍射仪(XRD)分析球磨后粉末的显微组织结构及物相,研究不同球磨时间对制备TiB_2-Ni(Al)复合粉末物相演变、组织结构的影响。研究结果表明,随着球磨时间的延长,延性金属Ni和Al变形程度逐渐增大,粉末中呈现Ni/Al交替混合组织结构,此种结构有利于金属在球磨过程中扩散形成Ni(Al)固溶体,且逐渐细化的TiB_2相嵌入至金属Ni和Al颗粒中。通过物相分析发现,随着球磨时间的延长,Al衍射峰强度逐渐降低,并发现在球磨时间为36h时形成Ni(Al)固溶体。     

Reactive mechanical grinding of magnesium in hydrogen and the effects of additives

The use of reactive mechanical grinding (MG under H₂) of magnesium powder improves the hydrogen sorption properties. The hydrogenation of Mg starts in situ during the milling process, thus circumventing the activation procedure that is generally required for Mg. The effects of the addition of various elements or compounds have been studied. The hydriding is determined to be a two-step process: nucleation and diffusion. A direct relationship exists between the nucleation duration and the specific surface area of the magnesium powder. A critical milling time exists up to which the diffusion process is improved and above which no more improvement is observed (the maximum internal stress in the powder is also reached at this critical time). The diffusion is controlled by the number of crystallites per particle that can be reduced by increasing the milling time up to 10 hr. The addition of Co (catalyst), YNi (hydrogen pump), or oxides (abrasive elements and nucleation centers) leads to an improvement of the hydrogen sorption properties (but a strong dependence upon the milling time is reported). Finally, the sorption properties of these mixtures are comparable with those reported for MgH₂-metal mixtures.     

Synthesis of TiC by controlled ball milling of titanium and carbon

Titanium and carbon powder mixtures with compositions of Ti_100−x C _x (x = 50, 40, 30) were milled under a helium atmosphere using a magneto ball mill. Controlled ball milling was performed in a higher energy impact mode and a lower energy shearing mode. For Ti₅₀C₅₀ and Ti₆₀C₄₀ powder mixtures milled in impact mode, TiC was formed via a mechanically-induced self-propagating reaction (MSR). When milling Ti₇₀C₃₀ in impact mode, the reaction to form TiC proceeded gradually as milling progressed; indicating that, for milling conditions that lead to the formation of TiC via MSR, a minimum carbon content is required to sustain the self-propagating reaction to form TiC. Milling in shearing mode resulted in the gradual formation of TiC during milling. This study found that increasing the carbon content of the starting powder mixture slowed the milling process. Replacing the activated carbon starting powder with high purity graphite was found to have little effect on the ignition time; indicating that the slowing of the milling process is not due to graphite acting as a lubricant during milling. Rather, this slowing of the milling process is most likely due to an increased carbon content resulting in an increase in the volume of the powder mixture. This would have a similar effect during milling to decreasing the ball:powder weight ratio (BPR), which is known to slow the milling process.     

Mechanically activated metathesis reaction in NaNH<Subscript>2</Subscript>–MgH<Subscript>2</Subscript> powder mixtures

The present work addresses the kinetics of chemical transformations activated by the mechanical processing of powder by ball milling. In particular, attention focuses on the reaction between NaNH₂ and MgH₂, specific case studies suitably chosen to throw light on the kinetic features emerging in connection with the exchange of anionic ligands induced by mechanical activation. Experimental findings indicate that the mechanical treatment of NaNH₂–MgH₂ powder mixtures induces a simple metathetic reaction with formation of NaH and Mg(NH₂)₂ phases. Chemical conversion data obtained by X-ray diffraction analysis have been interpreted using a kinetic model incorporating the statistical character of the mechanical processing by ball milling. The apparent rate constant measuring the reaction rate is related to the volume of powder effectively processed during individual collisions, and tentatively connected with the transfer of mechanical energy across the network formed by the points of contact between the powder particles trapped during collisions.     

晶态 Ni 粉与非晶 Fe_(78)Si_(12)B_(10)球磨时的固态反应

研究了晶态 Ni 粉与非晶 Fe_(78)Si_(12)B_(10)球磨时的固态反应。结果表明,当以(?)17at.-%Ni 和30at.-%Ni 与相应的非晶粉混合球磨后,产物为新的含 Ni 的完全非晶粉末。当以50at.-%Ni 与相应的非晶粉末混合球磨后,除了生成新的非晶相外,还有γ(Fe,Ni)相生成。     

Polymorphic transformation and powder characteristics of TiO2 during high energy milling

Many studies have indicated that the reactivity of reactants can be enhanced greatly by mechanical activation through high energy ball milling. To understand this enhanced reactivity, the polymorphic transformation and the evolution of the powder characteristics of TiO₂ and graphite mixtures during high energy ball milling was investigated using various analytical instruments. It was found that polymorphic transformation of anatase to srilankite and rutile took place during milling. Furthermore, amorphization of crystalline phases and crystallization of the amorphous phase occurred at the same time during milling. High energy milling also led to ultrafine crystallites, large specific surface areas, and substantial amounts of defects in the powder particles. Effects of the graphite addition and the milling temperature on the polymorphic transformation and the evolution of the powder characteristics were also investigated. It was proposed that the polymorphic transformation of TiO₂ during milling could be explained in terms of the temperature-pressure phase diagram if the temperature rise and high pressure at the collision site were taken into consideration.     

Effect of Mechanical Activation on the Packed-Bed, High-Temperature Behavior of Hematite and Graphite Mixture in Air

The present study reports the effect of mechanical activation on the reaction behavior of the Fe₂O₃/C powder mixture at high temperature under air atmosphere. Hematite and graphite were ground up to 150 hours using a ball mill with an alumina vial. The mixture was heated isothermally in the temperature range of 1173-1373°K using an electric furnace. The degree of reaction was determined by weight-loss measurement using a high accurate balance. It was found that low-energy mechanical milling at room temperature increases (the degree and) the rate of reaction at constant temperature. However, this effect was more significant at temperatures above 1273°K. At temperatures below 1273°K, the main reaction is oxidation of graphite and the total reaction process is controlled by diffusion of gases, whereas above 1273°K both chemical reaction (gasification reaction) and diffusion were controlling mechanisms. However, increasing milling time would shift the controlling mechanism from diffusion toward pure chemical reaction above 1273°K. It was observed that the mechanical milling might cause the mechanism to be changed at lower temperatures. This could be attributed to the increase of the rate of reaction due to mechanical milling. It was also observed that milling of powder mixture would decrease the difference in the average reaction rates at various degrees of reaction.     

新型高性能粉末冶金高速钢及其近净成形制备技术

目的研究无熔炼制备高性能近净成形粉末冶金高速钢的新工艺(SAP工艺)。方法以铁粉、钴粉和碳化物粉末为原料,通过机械球磨和真空活化烧结制备SAP 6031粉末冶金高速钢,并采用扫描电镜、X射线衍射、碳含量、相对致密度等检测方法,探讨球磨和活化烧结对试样致密化过程的影响。结果球磨后的原料粉末具有较高的烧结活性,结合后续活化烧结过程中的碳氧反应,使烧结坯在远低于液相线温度下实现烧结致密化(99.5%),材料力学性能优异,且杂质含量远低于标准值。结论 SAP工艺具有合金成分易调节、工艺流程短、生产能耗低、近净成形等优点,在特种粉末高速钢开发、异形件和非标件的灵活生产上具有显著优势。     

Role of intensive milling in mechano-thermal processing of TiAl/Al2O3 nano-composite

In this research a nano-composite structure containing of an intermetallic matrix with dispersed Al₂O₃ particles was obtained via mechanical activation of TiO₂ and Al powder mixture and subsequent sintering. The mixture has been milled for different lengths of time and then as a subsequent process it has been sintered. Phase evolutions in the course of milling and subsequent sintering of the milled powder mixture were investigated. Samples were characterized by XRD, SEM, DTA and TEM techniques.The results reveal that the reaction begins during milling by formation of Al₂O₃ and L1₂ Al₃Ti and further milling causes partial amorphization of powder mixture. DTA results reveal that milling of the powder mixture causes solid state reaction between Al and TiO₂ rather than liquid–solid reaction. Also, it was observed that the exothermicity of aluminothermic reduction is reduced by increasing the milling time and the exothermic peak shifts to lower temperatures after partial amorphization of powder mixture during milling. Phase evolutions of the milled powders after being sintered reveal that by increasing the milling time and formation of L1₂ Al₃Ti in the milled powder, intermediate phase formed at 500 °C changes from D0₂₂ Al₃Ti to Al₂₄Ti₈ phase.