高能球磨工艺对B4C/Al复合粉体结构演变及分布均匀性的影响

制备B4C增强Al基复合材料存在的难点主要是B4C颗粒在Al基体中的均匀分布及界面结合。本研究采用卧式搅拌高能球磨法制备了B4C/Al复合粉体,研究了搅拌轴转速和球磨时间对B4C/Al复合粉体结构演变及分布均匀性的影响。结果表明,随搅拌轴转速的提高,复合粉体受磨球碰撞时所获能量增大,增强体颗粒瞬间被破碎同时使Al粉发生较大的塑性变形,随球磨时间的延长,破碎的B4C颗粒逐渐在Al基体中分散均匀并与基体焊合,利于粉体实现均匀分布和良好的界面结合。球磨过程中B4C沿颗粒棱边脆性断裂,在Al粉的冷焊变形过程中被嵌入,形成一种片状化的Al粉基体包裹B4C增强相的复合粉体。在搅拌轴转速为600/800r/min(交变转速,交变频率为1min),球磨时间为2h时,B4C/Al复合粉体的粒度得到细化,B4C颗粒在Al基体中分布均匀、界面结合紧密。     

高能球磨法制备铜基电触头复合材料的研究

研究了高能球磨法在制备铜基电触头复合材料的工艺中对电触头的组织结构、力学性能和导电性能的影响,并对复合材料粉末中B4C颗粒的形貌、粒度以及在铜基体中的分布情况进行了研究.试验结果表明,高能球磨法对改变增强颗粒的形貌、改善增强颗粒体的分布均匀性非常有效,而且可以有效地提高触头材料的硬度和耐磨性.     

制备工艺对铝基复合材料增强体颗粒分布均匀性的影响

采用高能球磨法混料和低温快速热挤压相结合的粉末冶金工艺制备了SiCp/6066Al复合材料,研究了制备工艺对增强体颗粒分布均匀性的影响.结果表明:高能球磨法混料是显著改善增强体颗粒形貌、细化增强体颗粒粒度,在基体更小的微区域中实现增强体颗粒数量分布均匀性的最有效混料方法;低温快速热挤压利用基体的较低塑性和强大物理变形量使增强体颗粒进一步细化,得到的细小等轴颗粒更易随着基体的塑性流动而呈弥散均匀分布,进一步改善或消除微区域内增强体颗粒的偏聚或尽可能降低偏聚的程度.两种方法相结合是实现增强体颗粒微观分布均匀性的最有效方法.     

球磨制备轴承珠表面自润滑涂层及其摩擦性能

通过将MoS2粉末和轴承珠放入真空球磨罐中进行球磨的方法在轴承珠表面制备自润滑涂层。固定球磨转速为200r/min,研究不同球磨时间对轴承珠表面制备涂层的影响。采用配有能谱的扫描电子显微镜对球磨不同时间所制备涂层的形貌及元素分布进行观察。结果表明:随球磨时间的延长,涂层表面形貌变化不大,涂层厚度先增加后减小,Mo的分布先均匀后分散,球磨5h后涂层的厚度及元素的均匀性最佳。制备涂层的摩擦测试结果表明:球磨1h和5h所制备的涂层具有明显的润滑效果,而球磨10h的润滑效果不明显。球磨5h所制备的涂层具有最佳的润滑效果。     

高能球磨对Mg-Zn-Zr合金微观组织与力学性能的影响

在氩气条件下以400r/min高能球磨镁合金粉末,并将球磨后的粉末经过冷压—热压烧结—热挤压成型。研究了不同球磨时间的粉末以及挤压态样品的微观组织和力学性能。结果表明:随着球磨时间的延长,粉末颗粒尺寸可以细化到8μm,晶粒尺寸有效细化到34nm,在整个球磨过程中粉末有一定程度的氧化,并伴随有MgO纳米颗粒产生。粉末经过热压烧结—热挤压成型后,材料内部有MgZn2相颗粒析出,且均匀分布于Mg基体中。随着粉末颗粒的细化,材料性能得到改善,当球磨至10h时,粉末挤压态样品的极限拉伸强度为365 MPa,压缩屈服强度高达325 MPa,极限压缩强度保持在466 MPa。球磨至25h,颗粒平均尺寸细化至8μm左右,使得颗粒表面能大幅度增大,颗粒表面的氧化膜增厚,在热压烧结过程中阻碍了颗粒之间的结合,进而使得材料的力学性能恶化。     

球磨参数对ODS奥氏体不锈钢机械合金化效果的影响

为了研究球磨参数对ODS奥氏体不锈钢机械合金化效果的影响,以Fe、Cr、Ni、W、Ti纯金属元素粉末和纳米Y2O3为原料进行混合(配比为Fe-18Cr-8Ni-2W-1Ti-0.35Y2O3,质量分数),通过高能球磨的方式实现混合粉末的机械合金化.研究球磨时间、转速的变化对粉末粒度、成分均匀度和固溶程度的影响.结果表明,在真空环境下,球料比为10∶1、转速为380r/min、球磨时间60h时,粉末达到了很好的机械合金化效果,成分分布均匀;当球磨时间延长到100h时,粉末颗粒达到最细,继续球磨,粉末将出现明显的团聚.对最优机械合金化工艺参数获得的粉末进行热压致密化研究表明,随着温度的升高,试样的密度随之升高,维氏硬度随之降低.     

冷喷涂制备cBN-NiCrAl金属陶瓷涂层EI北大核心

采用机械合金化制备40vol%cBN-NiCrAl金属陶瓷复合结构粉末,采用冷喷涂制备了40%cBN-NiCrAl(体积分数)金属陶瓷复合结构涂层。研究了机械合金化过程对粉末的相组成、晶粒尺寸以及显微组织的影响。采用扫描电子显微镜和X射线衍射分别表征不同球磨时间下粉末以及冷喷涂涂层的显微组织和相结构。采用Scherrer公式估算不同球磨时间下粉末以及冷喷涂涂层中合金基体相的晶粒尺寸。结果表明,40vol%cBN-NiCrAl金属陶瓷粉末球磨40h后,基体的平均晶粒尺寸达到~50nm;复合结构涂层组织致密,硬质颗粒在合金基体中分布均匀。喷涂过程中,粉末相结构未发生变化,晶粒尺寸也未发生明显的长大。测试表明涂层的显微硬度约为1170HV0.3。     

高能球磨粉末冶金制备工艺对15%SiCp/2009Al复合材料性能的影响

采用高能球磨粉末冶金法制备了15%SiC_p/2009Al复合材料,研究了球磨转速、球磨时间、加热抽真空工艺、热压成型以及热挤压比对复合材料力学性能的影响。结果表明,球磨转速和时间、热压成型工艺是影响复合材料力学性能的重要因素。较长时间高转速球磨使SiC颗粒均匀分布,高温真空热压改善粉末之间的结合是获得高性能复合材料的关键。转速190 r/min、球磨6 h制备的复合粉末经高温真空热压、挤压后的复合材料SiC颗粒均匀分布,材料的抗拉强度高达650 MPa,延伸率大于5%。      

上海推出一种制备镁基复合材料的新工艺

上海交通大学张修庆等近日向社会推出一种制备镁基复合材料的新工艺。该工艺步骤如下：配制增强相反应体系粉末，采用机械球磨对反应体系粉末进行活化处理，通过控制球磨时间、转速、球料比来控制颗粒大小和储能，再将球磨处理的反应体系粉末压制成预制块；进行镁基体材料的熔炼，选取合适的熔体温度，将球磨反应体系粉末预制块熔解到镁熔体中，球磨粉末在镁熔体中发生原位反应形成增强相，再借助搅拌技术使颗粒分散均匀，进行反应体系的熔解反应过程；将熔体静置后浇铸，铸造成形。     

高体分SiC颗粒增强镁基复合材料的显微组织与力学性能EI北大核心

预先对SiC颗粒增强体进行表面氧化处理,然后采用压铸浸渗法制备了体积分数为51.5%的SiCp/Mg-6Al-0.5Mn复合材料。通过压缩性能测试、扫描电镜、透射电镜等方法,研究了复合材料的显微与力学性能。结果表明,在基体Mg-6Al-0.5Mn合金掺入51.5%体积分数的SiC颗粒预制块后,复合材料的组织致密,分布均匀,其断裂方式包括界面脱开、基体韧断和增强体开裂。SiC颗粒与基体之间发生了界面反应,生成了纳米级的Mg2Si化合物。同时,适度的预氧化可以提高基体与颗粒之间的界面结合强度,从而使复合材料抗拉强度得到提高。     

碳化硼颗粒增强Cu基复合材料的研究

研究了用表面涂覆含钛金属涂层的碳化硼颗粒增强Cu基复合材料[B4Cp/(TiB2 TiN)/Cu],并与未经涂覆的B4C颗粒增强Cu基复合材料（B4Cp/Cu)进行了对比。实验结果表明,前者的致密度和电导率比后者好。磨损实验结果表明,使用有涂层颗粒的复合材料的耐磨性比无涂层颗粒的好。通过对复合材料界面和磨损表面的电镜观察表明,B4C颗粒经过涂覆处理后,改善了复合材料的界面粘结性能,颗粒与基体间有良好的浸润性。     

高能球磨制备TiB_2/TiC纳米复合粉体

研究了通过高能球磨制备ＴｉＢ２／ＴｉＣ纳米复合粉体的反应过程和机理,对粉体的显微结构进行了表征．实验结果表明,采用金属 Ｔｉ和 Ｂ４Ｃ为原料,在球磨过程中, ＴｉＣ先于 ＴｉＢ２形成．球磨５ｈ后Ｔｉ与Ｂ４Ｃ反应生成ＴｉＢ２和ＴｉＣ,在随后的长时间高能球磨过程中ＴｉＢ２和ＴｉＣ两相保持稳定．球磨 ３０ｈ后,直径约 ８ｎｍ的 ＴｉＣ纳米粒子分布在 １００～２００ ｎｍ的 ＴｉＢ２粒子中,形成均匀分布的纳米ＴｉＢ２／ＴｉＣ复合粉体．     

Preparation and investigation of Al–4 wt % B<Subscript>4</Subscript>C nanocomposite powders using mechanical milling

Boron carbide nanoparticles were produced using commercially available boron carbide powder (0·8 μm). Mechanical milling was used to synthesize Al nanostructured powder in a planetary ball-mill under argon atmosphere up to 20 h. The same process was applied for Al–4 wt % B₄C nanocomposite powders to explore the role of nanosize reinforcements on mechanical milling stages. Scanning electron microscopy (SEM) analysis as well as apparent density measurements were used to optimize the milling time needed for completion of the mechanical milling process. The results show that the addition of boron carbide particles accelerate the milling process, leading to a faster work hardening rate and fracture of aluminum matrix. FE-SEM images show that distribution of boron carbide particles in aluminum matrix reaches a full homogeneity when steady state takes place. The better distribution of reinforcement throughout the matrix would increase hardness of the powder. To study the compressibility of milled powder, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B₄C particles. For better distribution of reinforcement throughout the matrix, r, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B₄C particles.     

Adiabatic shear instability based mechanism for particles/substrate bonding in the cold-gas dynamic-spray process

Particles/substrate interactions during the cold-gas dynamic-spray deposition process are studied using a dynamic axisymmetric thermo-mechanical finite element analysis. In addition, the particles/substrate bonding mechanism has been investigated using a one-dimensional thermo-mechanical model for adiabatic strain softening and the accompanying adiabatic shear localization. The results obtained show that the minimal impact particles velocity needed to produce shear localization at the particles/substrate interface correlates quite well with the critical velocity for particles deposition by the cold-gas dynamic-spray process in a number of metallic materials. This finding suggests that the onset of adiabatic shear instability in the particles/substrate interfacial region plays an important role in promoting particle/substrate adhesion and, thus, particles/substrate bonding during the cold-gas dynamic-spray process.     

Interfacial structure and strength on Ti(C,N) joint using liquid phase diffusion bonding with Ti/Ni interlayer

Abstract

Partial transient liquid phase diffusion bonding (PTLP-DB) on Ti(C,N) cermet was studied in the present paper using Ti/Ni/Ti foil sandwich structure as the interlayer. The interfacial structure and element distribution at the interface were observed using SEM, electron probe microanalysis and X-ray diffraction. The joint strength was measured using four-point bending test. The results showed that metallurgical bonding between Ti(C,N) cermet was achieved using PTLP-DB. Near Ti(C,N) cermet side, a strong chemical reaction occurred to produce an interfacial multilayer containing Ti–Al and Ti–Ni intermetallics. Different bonding times during PTLP-DB were also studied, and there was an optimum time during bonding. With a shorter bonding time, voids were observed at the interface, while with a prolonged time, the bending strength on the joints also decreased due to the overgrowth on intermetallic layer and the existence of high gradient residual stress at the interface.     

多重结构Ti-B4C/Al2024复合材料的组织和力学性能

为了研究多重结构对铝基复合材料力学性能的影响,将气雾化态Al2024合金粉末与球磨不同时间的Ti-10%(质量分数,下同)B_4C复合粉末混合,采用热压烧结和热挤压的方法制备多重结构Ti-B_4C/Al2024复合材料。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和拉伸试验机对不同材料的显微组织与力学性能进行观察和测试,并对多重结构复合材料的强韧化行为进行讨论。结果表明:Ti-B_4C/Al2024复合材料多重结构包括基体Al2024、核壳结构Ti/Al₁₈Ti_2Mg_3组织和B_4C颗粒。向Al2024中加入5%预先球磨6h后的Ti-B_4C粉末时,其屈服强度从107MPa提高到122MPa,并且表现出与热挤压Al2024合金几乎相同的伸长率。当球磨时间延长至12h时,试样5TB-12h的伸长率可达到16.4%。然而,复合材料的伸长率随着Ti-B_4C添加量的增加而降低。     

Effect of bismuth–tin alloy particle diameter on bonding strength of copper nanoparticles/bismuth–tin solder hybrid joints

The effect of the diameter of Bi–Sn alloy particles on the bonding strength of hybrid joints formed between SiC chips and direct-bonded copper (DBC) plates using a Cu nanoparticles/Bi–Sn solder was studied. The bonding strength was the highest at 40 MPa for a Bi–Sn alloy particle diameter of 10 µm. Further, the bonding strength was dependent on the area of the bonding layer adhering to the SiC-side fracture surface, as determined by the die-shear test. Ni, which was deposited on the SiC chips and DBC plates before the bonding process, remained near the interfacial area of the bonding layer in the joints formed using the 5 µm particles. In contrast, Ni diffused all over the bonding area, with the exception of the interfacial area where Cu–Sn compounds were formed, in the joints produced using the larger alloy particles. The distribution of Sn in the bonding layer became more uniform and the segregation of Bi at the interface became more pronounced as the particle size was reduced. Further, with an increase in the particle size, the Ag layers deposited on the surfaces of the SiC chips and DBC plates diffused into the bonding layer after the first firing step at 473 K, which was performed before the secondary firing step at 623 K. These results imply that the diameter of the Bi–Sn solder particles in hybrid joints affects the interfacial structure, as it governs the wetting behavior of the Bi–Sn solder and hence has a determining effect on the bonding strength.     

包覆混料对镀铜混合尺寸SiCp/Fe力学性能的影响

为探索提高SiCp/Fe力学性能的途径,采用包覆混料工艺,研究了该工艺对镀铜SiCp/Fe力学性能的影响,以及该工艺下增强粒子混合尺寸的影响.结果表明:包覆混料相比于普通混料,可显著改善SiC粒子在基体中分散的均匀性,而镀铜的作用是显著消除界面缺陷;性能的改善是包覆混料改善粒子分散性和镀铜改善界面结合的综合结果.对于体积分数30%SiCp/Fe的抗拉强度,通过包覆改善均匀性的贡献可提高7.2%,通过镀铜消除界面缺陷的贡献可提高12.5%,因此减少界面缺陷对颗粒增强复合材料力学性能的提高更重要.混合尺寸粒子对力学性能的增强效果明显高于其对应单一尺寸,这是由于小尺寸粒子能有效地提高基体的强度,而大尺寸颗粒更有效地承担载荷传递的作用.