Microstructures and properties of Cu-Cr-W composite coatings fabricated by surface mechanical alloying technique

Cu-Cr-W composite coatings were prepared by mechanical alloying(MA)method using different powder ratios,rotational speeds and milling time.The micro structures and chemical compositions of as-synthesized coatings were analyzed by scanning electron microscopy(SEM)and energy-dispersive spectroscopy(EDS).Phases of ball-milled powders were identified by X-ray diffraction(XRD).The results indicate that the coating fabricated with powder ratio of 40 wt%Cu-Cr-W has better surface and cross-sectional microstructures and higher microhardness.The comparisons of cross-sectional micro structures of the coatings fabricated at different rotational speeds suggest that rotational speed of 300 r·min-1is the optimal for fabrication the coating,and the optimal milling time for the formation of coating is 7 h.The results of microhardness test show that the hardness of the substrate is largely improved because of the as-fabricated coatings.The results of the friction and wear tests indicate that the wear resistance of the copper substrate is improved after the deposition of Cu-Cr-W coating on it.The coating fabricated for 7 h exhibits the lowest friction coefficient,indicating its favorable friction and wear resistance.The formation mechanism of the coating was elucidated.According to the investigations in this work,the Cu-Cr-W coating fabricated by MA method is considered to be effective to reinforce the copper substrate.

Fabrication of Porous Mg-Zn Scaffold through Modified Replica Method for Bone Tissue Engineering

Biodegradable scaffolds are essential parts in hard tissue engineering. A highly porous magnesium-zinc （Mg-Zn 4 wt.%） scaffold with different Mg-Zn powder to liquid media ratios （50 wt.%, 70 wt.% and 90 wt.%） and different concentrations of ethanol （0 vol.%, 10 vol.%, 20 vol.% and 40 vol.%） were prepared through modified replica method. The mechanical properties were assessed through compression test and the structures of scaffolds were examined by Scanning Electron Microscope （SEM）. Results show that, the increase in Mg-Zn powder to liquid media ratio （50 wt.% to 90 wt.%） in ethanol free slurry, increases the thickness of struts （37 lam to 74 lam） and the plateau stress （0.5 MPa to 1.4 MPa）. The results obtained from X-ray Diffractometry （XRD） and compression test indicate that consuming ethanol in liquid media of replica, results in higher plateau stress by 46% due to less Mg-water reaction and no formation of Mg（OH）2 in the scaffold. The results of porosity measurement indicate that water-ethanol mixture composition and different solid fractions have no significant effects on true and apparent porosities of the fabricated scaffolds.

Measuring powder flowability with a modified Warren Spring cohesion tester

The measurement of powder flowability is a major concern for most industrial processes that deal with the handling of bulk solids as raw materials, intermediates, or products. The development of devices that measure the flowability of non-aerated powders has not progressed as rapidly as might have been hoped since most research activities have been based on various types of shear testers intended to aid the design of hoppers. A new flowability indicator named as weighted cohesion （WS） is established using newly improved version of direct cohesion texture. A cornerstone of the proposed technique is that the procedure is automated, using a digital Warren Spring tester called Warren Spring-University of Malaya cohesion tester （WSUMCT）, thus making results operator-insensitive. Besides being a practical tool to diagnose the cohesion of experimental powders, the ratio between measured cohesion （using WSUMCT） and aerated density （using Hosokawa PT-S） provides us with a powerful technique to research fundamental particle internal cohesion forces directly and use these data to indicate the flowability. In this work, a series of fine （9.4μm） and coarse （60 μm） porous silica gel particle mixtures, and mixtures of fine （28μm） and coarse （72 μm） glass ballotini as well, were used as test powders. The results from these tests agree well with relative flowability determined on our newly driven indicator using WSUMCT. The validation of aerated weighted cohesion （WSA） as a flowability indicator was authenticated by comparing the conducted parameter with established measured Hausner ratio （HR） and angle of repose （AoR）.