Equiatomic Alloys Containing CuZr Fabricated By Powder Metallurgy And Properties

High entropy alloys(HEAs)as a new type of alloy are usually consisted of multi-major elements in equal or near equal atomic ratio,and their products are often composed of solid solution phases.The unique design concept,phase compositions and excellent properties of HEAs play an important role in researching on new materials.In this study,Cu50Zr50 was selected as prototype,and Al,Ti and Ni elements which are amorphous alloys commonly used,were selected and added to design equiatomic alloys containing CuZr,then the bulk alloys and coatings were synthesized by powder metallurgy method.Firstly,the equiatomic alloys powders and bulk alloys were synthesized by mechanical alloying(MA)and spark plasma sintering(SPS),respectively.Then the microstructures,hardness and corrosion resistance properties of alloys had been studied,and their mechanisms were investigated.Additionally,CuZrAlTiNi and CuZrAlTiNiSi/W HEAs coatings were prepared by hot press sintering(HPS)on the T10 steel substrate.Moreover,the microstructures,hardness,corrosion resistance and friction resistance properties of coatings were studied.In this work,the phase compositions,morphologies and properties of as-milling powders and sintered bulk alloys as well as coatings were investigated by X-ray diffraction,field emission scanning electron microscopy,differential scanning calorimetry,transmission electron microscopy,electrochemical workstation,Vichers' microhardness and friction and wear tester.The main results are as follows:1.The final products of as-milling CuZr(E2),Cu Zr Al(E3),CuZrAlTi(E4)and CuZrAlTiNi(E5)alloys powders are completely amorphous phases,and they have the better mechanical stability.The onset crystallization temperatures(Tx)of four kinds of amorphous alloys powders have the highest value of 692 ?,indicating the better thermal stability.Moreover,E2 and E5 alloys firstly form amorphous phases at 20 h milling time,and have the higher amorphous forming ability.2.Equiatomic bulk alloys containing CuZr with metallic luster and high density are successfully prepared by SPS.Phase compositions: E2-520 ? bulk alloy is amorphous matrix composite;E3 and E4 bulk alloys are composed of solid solutions and intermetallic compounds;E5 bulk alloys sintering at different temperatures are both consisted of BCC,FCC1,FCC2 and AlNi2 Zr intermetallic compound,indicating the better phase stability.Composition distributions and densities: Cu element is mainly distributed in the phase boundaries of E2 and E3 bulk alloys at high sintering temperature,however,Cu,Zr and Ti elements are relatively evenly distributed in the boundaries of E4,presenting the addition of Ti can hinder the segregation of Cu element;E5 bulk alloy has uniform compositions and fine precipitates with nano size distributed uniformaly in the matrix,and possesses the highest density(99.8 %).Electrochemical seawater corrosion resistance and microhardness: E5-620 ? bulk alloy has the highest corrosion potential,the lower corrosion current and the wider passivation area,indicating the better overall corrosion resistance;E5-950 ? bulk alloy possess the widest passivation area,indicating the better pit corrosion resistance;E4-1100 ? bulk alloy has the highest hardness value(1173 HV0.2),which is main attributed to high sintering density(99.6 %)and the enhancement of nano precipitates.3.E5 high entropy alloy coating successfully synthesized by hot press sintering method on T10 steel substrate is composed of FCC1,FCC2,BCC and AlNi2 Zr intermetallic compound.The microhardness of coating surface is 943 HV0.2,which is about 3.5 times of that of the T10 steel substrate(269 HV0.2).The results are due to the enhancement of nano precipitates,phase interface strengthening and solid solutions strengthening.Additionally,the corrosion resistance in seawater solution of coating is better than substrate and the friction resistance of coating is slightly better than that of substrate.4.CuZrAlTiNiSi(E6-Si)high entropy alloy powder prepared by mechanical alloying has completely amorphous phase,and E6-Si high entropy alloy coating is also successfully synthesized by hot pressing sintering method on T10 steel substrate.The coating is composited of FCC,BCC solid solutions and different intermetallic compounds.The hardness(927 HV0.2)and seawater corrosion resistance of E6-Si high entropy alloy coating are significantly better than those of the substrate,but worse than E5 high entropy alloy coating,indicating that the uniform nano precipitates lead to the excellent properties of E5.Moreover,the preparation of CuZrAlTiNiW(E6-W)high entropy alloy coating is studied.The mechanical alloying powder consists of a single BCC solid solution phase.E6-W high entropy alloy coating is composed of two kinds of BCC solid solutions and AlNi2 Zr intermetallic compound.The hardness,corrosion resistance and friction resistance of coating are also better than those of the substrate.