Study On Preparation And Properties Of Porous Metal Bonded Abrasives

Metal bonded diamond grinding tools are often used to grind hard and brittle materials such as cemented carbide,advanced ceramics and natural granite.The metal bonded diamond grinding wheel prepared by traditional hot pressing sintering process has the characteristics of long service life,good compactness of sintering binder and good wear resistance,etc.However,the higher density will bring a series of problems to the metal bonded diamond grinding wheel during grinding,such as poor self-sharpening,easy burning of workpiece surface,and difficult to trim.Therefore,how to solve the above problems and improve the machining efficiency and performance of metal bonded diamond grinding tools during grinding has become a hot research topic in recent years.One of the effective methods to solve this problem is to make holes in the metal bond.In this thesis,four pore-forming agents such as titanium hydride,sodium chloride,sodium carbonate and sodium bicarbonate are added to copper-zinc metal bond,and porous metal bond diamond grinding tools are prepared by using pore-forming mechanisms such as thermal decomposition of pore-forming agent,dissolution of pore-forming agent,and die-pressing method.The porosity is controlled by changing sintering temperature,controlling the decomposition rate of pore-forming agent and changing the content of pore-forming agent.The relationship between pore morphology and bending strength,impact strength,hardness,abrasive strength loss rate,grinding ratio and grinding quality were studied.The experimental results are as follows:(1)Adding titanium hydride pore-forming agent can refine grains and toughen and strengthen Cu60Zn40 metal bond.When the optimum sintering temperature is 680?and titanium hydride content is 10vol%,the comprehensive properties are the best(bending strength is 445MPa,impact strength is 54.34k J/m²,hardness is HRB78,porosity is 4.86%).SEM results show that pores exist at the grain boundary of the binder,and the stoma is irregular.(2)Choosing titanium hydride as the pore former to prepare porous metal bond diamond abrasive tools.Titanium element was enriched around diamond and a small amount of strong carbon compound was produced,which effectively increased the bonding force between the bond and diamond abrasive.Take model Y316 cemented carbide as the grinding experiment for grinding parts.The best titanium hydride content was 10%,the friction coefficient was stable,the wear ratio R reached 61.67,and the burn phenomenon of cemented carbide surface was improved.(3)The study of adding pore-forming agents such as sodium chloride,sodium carbonate and sodium bicarbonate into the copper-zinc metal bond shows that all three pore-forming agents can play an obvious role in pore-forming in the bond,and the maximum porosity can reach 8.82%.After adding pore-forming agent,the strength and hardness of Cu-Zn metal bond decreased.The order of strength was as follows:the pore-forming agent with sodium chloride had the best strength,followed by sodium carbonate,and the sample with sodium bicarbonate had the worst strength.SEM and metallographic results show that the pore shapes formed by different pore-forming agents in Cu60Zn40-based metal bonding agents are different.The pore shapes of NaCl pore-forming agents are spherical,Na₂CO₃ pore-forming agents are oblate,and NaHCO₃ pore-forming agents are irregular splitting shapes.The compression pore-forming method can slow down the decrease rate of bonding strength.(4)After adding sodium chloride,sodium bicarbonate and sodium carbonate as pore-forming agents,the bending strength of the grinding tool decreased,but its grinding performance was effectively improved.The observation of fracture micro-morphology of grinding tool shows that there are a large number of holes and micro-cracks in the binder after the dissolution of pore-forming agent,which will lead to the reduction of the binding area around the diamond and reduce the holding power of the binder to the diamond,so the strength decreases.The wear test shows that the grinding ratio is higher than that of abrasive tools without pore-forming agent,and the maximum grinding ratio are 75.33,65.33 and 59.34.When the amount of soluble salt pore-forming agent is15vol%,there is no burn on the surface of the workpiece,and the surface quality of the workpiece is improved compared with that without pore-forming agent grinding tools.