| Tungsten alloy is a type of two-phase metal fabricated by powder metallurgy process,tungsten particles as the main component,due to its high density,high melting point,excellent corrosion resistance and strong radiation shielding ability,widely used in aerospace,weapons,nuclear industry,medical and other fields.Owing to its special characteristics such as coarse grains,brittleness at room temperature,easy to adhesion and high brittle-plastic transition temperature,serious tool wear happens in tungsten alloy cutting process,lead to high machining cost,poor quality and low efficiency.However,research on tool wear of tungsten alloy machining is rarely and its wear mechanism is still unknown.With high surface hardness,erosion resistance,good thermal stability,low comprehensive cost and other excellent properties,coated carbide tools used widely in hard-to-machine materials.Therefore,this paper focuses on the study of tool wear behavior of coated carbide tools in tungsten alloys machining.In view of the current status that the properties characterization method for commercial coated carbide tool is immature,characterization methods for the physical and chemical properties were proposed,then properties tests were carried out.Failure mode and adhesion force of chosen tools were analyzed by scratch test.Wear resistance and coating failure modes were compared by friction and wear test,and the causes of different resistance ability were analyzed.Relationship between the wear behavior of the tool,mechanical properties and scratch performance of the coating was established.It was pointed out that tools for tungsten alloy machining should with high bond strength and balanced mechanical properties of the coating?wear resistance and toughness?.Main works are drawn as follows:?1?Physical and chemical properties inspect:Necessary properties of the tool for tungsten alloy machining was analyzed according to existing research results,5 coated carbide tools?KC5010,KC5410,KCU10,AC510U,GC1115?and one without coating?K313?were selected.Physical and chemical properties characterization method for commercial tools were proposed for the first time.The results indicated that stripe and defect distributed on the surface,all the 6tools were cemented carbide tools and their hardness distributed from 1900Hv to 2000Hv.GC1115 had the thickest coating while AC510U's was the thinnest,nano-indentation test indicated that the coating increased surface hardness of the tools,the element composition test showed that KC5410 tool was TiB2 coating,and the others were TiAlN series coating with different Al/Ti ratio,contained a small amount of Cr,Si.Above test fully characterized the similarities and differences between the chosen tools,which lays a foundation for follow research work.?2?Scratch test:scratch test was carried out with automatic coating adhesion scratch tester.The result showed different adhesion force between chosen tools,KC5010,GC1115 and AC510U showed much higher adhesion force than KC5410 and KCU10,also different failure mode and ductile-brittle properties.Scratch test provided failure mode and adhesion force of chosen tools,as theoretical basis to analyze friction and wear test behaviors.?3?Friction and wear test apparatus:Existing friction and wear testing machine are difficult to meet the requirements of commercial tool wear resistance test,besides,its friction pair don't match well with actual situation.To solve above problems,friction and wear test apparatus were designed and built based on 4-component dynamometer and triaxial milling machine tool,then its parameters were calibrated by FEM simulation and experiment ways.The apparatus imitates the contact forms of tool-chip and tool-workpiece in actual machining,making the test results more closer to actual situation,with better accuracy and high efficiency for commercial cutting tool testing,satisfying the needs of high speed,high load friction and wear test.?4?Friction and wear test and analysis:Coating to tungsten alloy friction and wear test carried out on friction and wear test apparatus.Test results indicated that wear resistance disparities exist between chosen tools,the wear resistance ability was AC510U,KC5010,GC1115,KC5410,K313,KCU10 from strong to weak,the tribological properties and reasons of different wear resistance ability were analyzed.Results showed that the tribological properties significantly related with the scratch test performance,mechanical properties and ductility of the coating.Then tungsten alloy turning experiment was carried out with KC5010 and AC510U.The results showed that the AC510U tool has better durability in tungsten alloy turning than the KC5010.It proved that the AC510U tool has better wear resistance than KC5010. |
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