碳钢上激光辅助沉积Co-285合金的组织与性能

利用激光辅助直接金属沉积技术在1018低碳钢上沉积Co-285单壁墙,并利用优化参数制得大面积沉积层。利用光学显微镜、附带能谱仪的扫描电镜、X射线衍射仪、显微硬度计和磨损试验机研究沉积单壁墙或沉积层的显微组织、成分、物相、横截面的显微硬度分布和耐磨性。结果表明:沉积的单壁墙无气孔和裂纹等缺陷,成形性能良好,且与基体形成冶金结合;单壁墙由枝晶和枝晶间共晶组成;所有工艺参数下单壁墙的硬度相差不大;当激光功率为0.8kW、送粉率为8.6g/min、扫描速度为0.375m/min时,单壁墙硬度值最大,达到407HV0.5;在此参数下制得沉积层的组织与单壁墙的类似,其相组成为α-Co固溶体、富Cr的M23C6和Co3W;磨损60min后,沉积层体积损失为1.4mm3;磨损机制为研磨磨损、粘着磨损和氧化磨损的混合磨损。

Brazeability evaluation of Ti-Zr-Cu-Ni-Co-Mo filler for vacuum brazing TiAl-based alloy

Ti-47Al-2Nb-2Cr-0.15B(mole fraction,%)alloy was vacuum brazed with amorphous and crystalline Ti.25Zr-12.5Cu-12.5Ni-3.0Co-2.0Mo(mass fraction,%)filler alloys,and the melting,spreading and gap filling behaviors of the amorphous and crystalline filler alloys as well as the joints brazed with them were investigated in details.Results showed that the amorphous filler alloy possessed narrower melting temperature interval,lower liquidus temperature and melting active energy compared with the crystalline filler alloy,and it also exhibited better brazeability on the surface of the Ti.47Al.2Nb.2Cr.0.15B alloy.The TiAl joints brazed with crystalline and amorphous filler alloys were composed of two interfacial reaction layers and a central brazed layer.Under the same conditions,the tensile strength of the joint brazed with the amorphous filler alloy was always higher than that with the crystalline filler alloy.The maxmium tensile strength of the joint brazed at 1273 K with the amorphous filler alloy reached 254 MPa.

Density Assessment of Different Metals and Alloys by Gamma-Ray Transmission Technique via Using Co-60 Radioactive Source

In this study, density measurements were observed by using gamma transmission technique. Co-60 gamma emitter was used as gamma radioisotope source. Regarding the gamma-ray transmission method, initial radiation intensity （I0） and radiation intensity （I） determined experimentally and [I/I0] rates were calculated and then density of materials could be determined by using Beer-Lambert Equation. Experimental application performed on widespread industrial metals or metal alloys e.g. lead, copper and steel, brass. With this study, it is shown that gamma transmission technique can be used for density measurements.

Microstructure and properties of ultra-fine tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering

The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.After 15 h milling,the average W grain size in the powders is decreased to 120 nm.For the powders milled for 15 h,the density,hardness and transverse rupture strength of the alloys sintered only by an intensive pulse electric current are the maximum.When the total sintering time keeps constant,the properties of the sintered alloys can be obviously improved by optimizing the sintering time of pulse-and constant-currents.A bulk ultrafine alloy with an average W grain size of about 340 nm can be obtained by sintering 15 h-milled powders in a total sintering time of 6 min.The corresponding sintered density,hardness and transverse rupture strength reach 16.78 g /cm3,HRA84.3 and 968 MPa,respectively.

Comparison of surface integrity for dry and wet drilling of 49Fe-49Co-2V alloy

Working performances of the components made out of 49Fe-49Co-2V alloy are closely related to the surface integrity of the drilled holes,which are influenced remarkably by the cooling conditions.The present study focuses on the surface integrity differences between wet and dry drilled 49Fe-49Co-2V alloy holes.The drilled hole surface roughness and topographies,metallurgical and mechanical properties,and the exit characterizations were obtained using optical microscopy(OM),scanning electron microscopy(SEM),electron backscatter diffraction microscopy(EBSD),transmission electron microscopy(TEM),energy dispersive spectroscopy(EDS)and Vickers hardness techniques,etc.The effects of cooling conditions on the surface integrity were concluded and the influence mechanisms were analyzed based on the force and temperature differences in drilling process with different cooling conditions.It is found that the surface roughness and the thickness of refined-grain region of the dry drilled holes are larger than those of wet drilled holes;work hardening induced by wet drilling is more serious than dry drilling;chippings occurred in the exits of the wet drilled holes due to the material brittleness,which could be avoided by dry drilling.The surface integrity differences of wet and dry drilled holes are closely related to the force and temperature differences in drilling process with different cooling conditions.

Electrochemical properties of Co-S/x wt.% AB_5 composite materials

The Co-S/x wt.% AB5 （x=0, 10, 20, 30） composite materials were prepared by simply mixing Co-S material fabricated by hy- drothermal method and AB5 alloy. The structure and morphology of the composite materials were characterized by XRD and SEM, respectively. The electrochemical properties of the composite electrodes were studied by the galvanostatic charge, dis- charge test and electrochemical impedance spectroscopy. The results showed that the Co-S/20 wt.% AB5 composite electrode showed the highest discharge capacity and the best cycling stability. The existence of the AB5 alloy improved the electro- chemical activity of composite electrodes, reduced the electrochemical polarization resistances and promoted the electrochem- ical conversion reaction between Co and Co（OH）2. In order to improve the utilization rate of active materials, 0.0! mol/L Na2S203 was added into the electrolyte. The electrochemical properties of the composite electrode were significantly enhanced. After fifty cycles, the discharge capacity of the composite electrode increased from 407 to 481.7 mAh/g and the capacity reten- tion increased from 79.7% to 91.2%.