Enhanced Phase Size Adjustment And Its Effect On The Properties Of Al₂O₃/W-Cr Composites

Al2O3/W-Cr composite material has become one of the best materials to replace H13 die steel due to its high strength,high hardness,and high wear resistance.However,the disadvantages of Al2O3 particles are easy agglomeration and inhomogeneous distribution.Therefore,in this paper,the chemical dispersion method combined with two mechanical crushing methods were used to inhibit the agglomeration of the precursor composite powder,and the Al2O3/W-Cr composite material was obtained by vacuum hot pressing sintering.Phase analysis and microstructure characterization were carried out,and the relative density and hardness were tested,and the best dispersion process was determined.Subsequently,the influence of the particle size and content of Al2O3 on the relative density,hardness and flexural strength of the composite was discussed.Finally,the friction and wear properties of the composite materials were studied by friction and wear tests and the wear mechanism was analyzed.The main conclusions are as follows:(1)Different types and contents of dispersants have obvious effects on the particle size of Al(OH)3 colloid.When 10vol.%cetyl trimethyl ammonium bromide(CTAB)is added,the dispersion effect is the best,followed by 2wt.%polyethylene glycol(PEG),and 5vol.%sodium dodecyl sulfonate(SDS)is the worst.For composite materials,non-ionic dispersant PEG has the best dispersion effect.Al2O3 particles are reduced by 58.7%compared with without dispersant,and the relative density and hardness of composite materials are the highest.At the same time,the type of dispersant has a significant effect on the dispersion of Cr elementary substance.When the anionic dispersant SDS is added,a large amount of segregation of Cr powder occurs.(2)Both mechanical vibration dispersion and wet ball milling can refine the size of Al2O3 particles to a certain extent.But in comparison,the refining effect of mechanical vibration dispersion is more significant.The main reason is that the high energy of planetary ball milling causes the Al(OH)3/W-Cr composite powder to agglomerate and reduce the specific surface area.When 2wt.%PEG and mechanical vibration dispersion for 4 h is used to prepare composite materials,Al2O3 has the smallest particle size,61.30%less than without dispersant,and the relative density and hardness reach the best values,99.99%and 997.42 HV,respectively.(3)The composite is composed of W,Cr and Al2O3 phase,in which Al2O3 is generated in situ from Al(OH)3.Two kinds of solid solutions rich in W-(W,Cr)ss and rich in Cr-(Cr,W)ss can be formed simultaneously by Cr and matrix W,and the solid solution(Al,Cr)2O3 with α-Al2O3 structure can be formed by Cr and Al2O3.A metallurgical bonding interface is formed,which effectively connects the matrix and the reinforcing phase,and improves the bonding strength of the composite material to a certain extent.(4)As the content of Al2O3 increases,the size of the composites shows an increasing trend.The relative density of the composites reaches more than 99%,which is increased by more than 1%compared with W-Cr alloy.The main reason is that the addition of Al2O3 reduces the activation energy of sintering.In addition,the hardness and flexural strength of the composite material first increase and then decrease with the increase of the Al2O3 content.When the Al2O3 content is 10vol.%,the hardness and bending strength reach the optimal value,which increases by 16.2%and 28.57%compared with W-Cr alloy,respectively.This is mainly due to the fine grain strengthening.At the same time,after calculation,when the content of Al2O3 exceeds 10.41vol.%,the Al2O3 will start to aggregate,forming weak bonding interface and making it easy to fall off,which explains the change of composite properties.(5)The wear rate and friction coefficient of Al2O3/W-Cr composites first decrease and then increase with the increase of Al2O3 content.When the content is 10vol.%,the wear rate and friction coefficient are the smallest,and the wear resistance is the best.The main reason is that the proper amount of Al2O3 particles improves the hardness and is not easy to fall off.The wear mechanism of the material is mainly from abrasive wear,supplemented by adhesive wear,and gradually changes to abrasive wear and alumina shedding,accompanied by adhesive wear.