Study On The Regulation Of Copper Infiltrated Alumina And Al₂O₃/cu Composites

Alumina?Al₂O₃?has good characteristics of high melting point,high hardness and good chemical stability,but its low fracture toughness and poor thermal conductivity have seriously limited its wide-range engineering applications.Whereas a metal such as copper has excellent electrical and thermal conductivities,but has low yield strength/hardness and poor wear resistance.Al₂O₃/Cu composites can take both the advantages of good thermal and electrical conductivity,high strength,hardness and wear resistance.Because of the poor wettability of metal Cu and Al₂O₃,the mechanical mixing and sintering of the two will lead to the separation at the interface.In order to solve this problem,this paper starts with the material powders and the sintering method on the basis of related research.Ni@Al₂O₃ coated powders were prepared by heterogeneous precipitation method and Cu@Al₂O₃ coated powders were prepared by thermal chemical plating in order to improve the wettability between them.The influence factors in the plating process are analyzed and discussed in order to get the compound powder which is in accordance with the requirement of the composition and the good coating effect.Al₂O₃/Cu?15 vol%Cu?composite was obtained by SPS sintering.In addition,mechanical mixing powder and ordinary infiltration sintering were used as the control group.The relationship between the fracture toughness,hardness,relative density and electrical resistivity of the composites,the morphology and the process of the composites were discussed and analyzed by means of XRD,SEM,XPS and wettability test.The effects of the coating on the morphology,mechanical properties and interface mechanism of the composites were analyzed.The following conclusions were obtained:?1?Al₂O₃ with the average particle size of 1?3?m and NiSO4·6H2O,NH4HCO3 powders were used as raw material powders.The Ni@Al₂O₃ coated powders with uniform microstructure can be successfully prepared by heterogeneous precipitation,by controlling the concentration of NiSO4·6H2O solution at 0.06 mol/L,PH=8 and temperature at 20?25 0C.The median diameter of the composite powder is 3.39 ?m,the thickness of the coating is about 0.3 ?m.And it has certain magnetic properties and conductivity.?2?Coarsening and activation sensitization of Al₂O₃ powder before plating,using CuSO4·6H2O as Cu salt,formaldehyde solution?HCHO?as reducing agent,and double complexing agent were?C4H4O6KNa·4H2O and EDTA-Na?.By controlling PH=12?13,content of stabilizer K4[Fe?CN?6]is 10 mg/L and at room temperature,Cu@Al₂O₃ coated powders with complete coating and uniform coating can be successfully obtained by electroless plating.?3?The composites prepared by infiltration sintering without external pressure at 1350 ?under an argon atmosphere were loosely compacted.The solidified molten Cu particles were distributed inside the Al₂O₃ matrix and thefracture morphology showed a brittle fracture feature.The relative density of Al₂O₃/Cu composite was 82.5%,with a hardness of 693 HV fracture toughness of 4.21 MPa·m1/2,the resistivity of 1.120 ?·m.In the presence of an external pressure of 30 MPa in the SPS process,the microstructure of the composite was compact,and copper phases were distributed uniformly inside the alumina matrix.The fracture surface showed a characteristic of quasi-cleavage type.Whereas those of the relative density of SPS ones was 99.1%,with hardness of 842 HV,fracture toughness of 6.50 MPa·m1/2,and resistivity of 2*10-3 ?·m.?4?Al₂O₃/Cu composite material was obtained by SPS sintering with Ni@Al₂O₃ coated powder as raw material.The microstructure is dense and the phases are evenly distributed.The alumina ceramic phase forms a skeleton structure,and Cu is infiltrated into the ceramic skeleton structure to form a three-dimensional network-like.The fracture surface showed a characteristic of quasi-cleavage type.The properties of the composites are as follows:the hardness is 878 HV,the fracture toughness is 6.72 MPa·m1/2,the resistivity is 1.28*10-3?·m,and the relative density is 99.3%.The presence of the Ni coating makes the wetting angle between the ceramic Al₂O₃ and Cu decrease from 128° to 86.2°.?5?The Al₂O₃/Cu composites were obtained by SPS sintering using Cu@Al₂O₃ coated powders as raw materials.The distribution of the metal phase and the ceramic phase is uneven,and the agglomeration phenomenon in the copper phase leads to the discontinuity of the ceramic skeleton.The fracture surface showed a characteristic of quasi-cleavage type.The properties of the composites are as follows:the hardness is 827 HV,the fracture toughness is 5.88 MPa·m1/2,the resistivity is 1.528 ?·m,and the relative density is 95.2%.