Microstructural Features and Properties of High-hardness and Heat-resistant Dispersion Strengthened Copper by Reaction Milling

The oxide dispersion strengthened copper alloys are attractive due to their excellent combination of thermal and electrical conductivities,high-temperature strength and microstructure stability.To date,the state-of-art to fabrication of them was the internal oxidation （IO） process.In this paper,alumina dispersion strengthened copper （ADSC） powders of nominal composition of Cu-2.5 vol%Al2O3 were produced by reaction milling （RM） process which was an in-situ gas-solid reaction process.The bulk ADSC alloys for electrical and mechanical properties investigation were obtained by sintering and thereafter hot extrusion.After the hot consolidation processes,the fully densified powder compacts can be obtained.The single γ-Al2O3 phase and profile broaden effects are evident in accordance with the results of X-ray diffraction （XRD）;the HRB hardness of the ADSC can be as high as 95;the outcomes should be attributed to the pinning effect of nano γ-Al2O3 on dislocations and grain boundaries in the copper matrix.The electrical conductivity of the ADSC alloy is 55%IACS （International Annealing Copper Standard）.The room temperature hardness of the hot consolidated material was approximately maintained after annealing for 1 h at 900 ℃ in hydrogen atmosphere.In terms of the above merits,the RM process to fabricating ADSC alloys is a promising method to improve heat resistance,hardness,electrical conductivity and wear resistance properties etc.

Hydriding and microstructure nanocrystallization of ZK60 Mg alloy by reaction milling in hydrogen

The hydriding of as-cast Mg-5.5%Zn-0.6%Zr(ZK60 Mg)(mass fraction)alloy was achieved by room-temperature reaction milling in hydrogen,with the mechanical energy serving as the driving force for the process.The hydriding progress during milling was examined by hydrogen absorption measurement,and the microstructure change was characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM),respectively.The results show that,by room-temperature reaction milling in hydrogen,the as-cast ZK60 Mg alloy can be fully hydrided to form a nanocrystalline MgH_(2) single-phase microstructure.In particular,the average grain size of the MgH_(2) phase obtained by room-temperature reaction milling in hydrogen for 16.2 h is about 8-10 nm,and the average particle size of the as-milled hydrided powders is 2-3μm.

Rapid synthesis of MoSi_2-Si_3N_4 nanocomposite via reaction milling of Si and Mo powder mixture

The nanocomposite of MoSi2-SiaN4 （molybdenum disilicide-silicon nitride） was synthesized by reaction milling of the Mo and Si powder mixture. Changing the processing parameters led to the formation of different products such as a- and B-MoSi2, SiaN4, Mo2N, and M05Si3 at various milling times. A thermodynamic appraisal showed that the milling of Moa2Siss powder mixture was associated with highly exothermic mechanically induced self-sustaining reaction （MSR） between Mo and Si. The MSR took place around 5 h of milling led to the formation of a-MoSi2 and the reaction between Si and N2 to produce Si3N4 under a nitrogen pressure of 1 MPa. By increasing the nitrogen pressure to 5 MPa, more heat is released, resulting in the dissociation of Si3N4 and the transformation of a-MoSi2 to β-MoSi2. Heat treatment was also performed on the milled samples and led to the formation of Mo2N and the transformation of a-MoSi2 to β-MoSi2 at the milling times of 10 and 40 h, respectively.

Preliminary Investigation of NiAl-TiB_2 Composite Prepared by Reaction Milling

Reaction-milled NiAl-TiB2 composite was fabricated by mechanical alloying elemental powders and hot pressing. TiB2 particles are distributed mostly in grain boundaries of the matrix. The compressive strain to failure of the composite at RT is about twice that of cast NiAl. The compressive yield stress at high temperatures is about 4.5 times higher than that of extruded NiAl, and is also much stronger than XD NiAl-TiB2 composites. Deformation behavior between 1000~1100℃ with different strain rates has been investigated

Ball-milling MoS_2/carbon black hybrid material for catalyzing hydrogen evolution reaction in acidic medium

Replacing platinum for catalyzing hydrogen evolution reaction （HER） in acidic medium remains great chal- lenges. Herein, we prepared few-layered MoS2 by ball milling as an efficient catalyst for HER in acidic medium, The activity of as-prepared MoS2 had a strong dependence on the ball milling time, Furthermore, Ketjen Black EC 300J was added into the ball-milled MoS2 followed by a second ball milling, and the resultant MoS2/carbon black hybrid material showed a much higher HER activity than MoS2 and carbon black alone. The enhanced activity of the MoS2/carbon black hybrid material was attributed to the increased abundance of catalytic edge sites of MoS） and excellent electrical coupling to the underlving carbon network.

Microstructure characterization and hydrogen desorption behaviors of Mg-Al-H powders prepared by reactive milling in hydrogen

Microstructure and phase evolutions of Mg-A1 powders ball milled in hydrogen atmosphere were investigated. Both in Mg-3%A1 （mass fraction） and Mg-9%AI systems, fl-MgH2 phase was observed upon a short milling time of 4 h and its maximum content of-80% was reached after 32 h. Neither as-milled powders of the in the two systems contain Mgl7All2. However, heating the milled powders of Mg-9%AI powders to 350 ~C resulted in the precipitation of Mg17A112. DTA/TG analyses of those powders milled for 8-40 h showed that either well-developed peak doublets or shoulders were observed, which plausibly corresponded to the separate hydrogen desorption from different particle fractions offl-MgH2.

Microstructure-Property Correlation in AI_4C_3 Dispersion Strengthened Al Composite

The microstructure and tensile properties of Al_4C_3 dispersion strengthened Al composite fabricated by reaction milling technique were investigated.It is indicated that the rod-like Al_4C_3 dispersoids having a diameter of 0.02-0.03 μm and a length of 0.1-0.3μm are formed by reaction of C with Al, and uniformly distributed in the Al matrix.The interface between Al_4C_3 and Al is clean and the interfacial bonding is good.The matrix consists of the subgrains which have the size of 0.3-0.4μm, and most of the Al_4C_3 dispersoids are distributed on the subgrain boundaries.The 11 vol.-% Al_4C_3/Al composite exhibits an UTS (ultimate tensile strength) of 400 MPa and an elongation-to-failure of 8.0%.