Preparation Of Ni-W-P-Si₃N₄ Electroless Composite Coating And Its Application In Twist Drill Cutting Tools

The chemical composite coatings have been widely used in aerospace,vehicles and other field due to their excellent physical and chemical properties,such as good hardness,high-wearing resistance,low friction coefficient,good chemical stability.In order to improve durability of high speed steel cutter,the hardness and wear properties of Ni-W-P ternary alloy coating and the composite coating that embed silicon nitride nanoparticles in were studied.Then,in order to take full advantage of the Ni-W-P-Si₃N₄ composite coating,the binding force between the coating and high speed steel cutter were researched in the paper,too.In the end,the investigation on the working durability of the twist drills,including the high speed steel naked cutter,the cutters with Ni-W-P coating and Ni-W-P-Si₃N₄ composite coating,respectively,were carried out.The researches show that the effect is positive.Compared with the Ni-P binary alloy coating,the Ni-W-P coating has higher hardness and better wear resistance.In this paper,Ni-W-P coatings with different contents of W and P were prepared by changing the amount of sodium tungstate added in electroless plating bath?0-75g/L?.The W and P contents of the coatings were analyzed by scanning electron microscope and energy spectrum analyzer.The hardness of the coating was tested by a microhardness tester,and the friction coefficient and wear rate of the coating were tested with a ball-disk friction wear tester.The hardness of the coating was compared with the W,P content of the coating to study the internal relationship between them;and through the X-rays The diffractometer analyzes the phase of the coating and explores the relationship between W and P content and the typical phase in the coating,and then relates to the hardness and wear resistance of the coating.Using the same method,the chemical composition and coating of the coating under the aging treatment are studied.The relationship between hardness and wear resistance.The preparation process of Ni-W-P-Si₃N₄ composite coating was optimized.On the basis of determining the deposition method as alternate deposition,the effect of alternate deposition time on the content of Si₃N₄ in the coating was studied.The optimal alternate deposition time was optimized;In the above,the effect of Si₃N₄ addition amount and particle size on the morphology,composition and hardness of the composite coating was investigated.The results show that the content of Si₃N₄ is the highest in Ni-W-P-Si₃N₄ bath deposition for 2 min and Ni-W-P bath deposition for 1 min.For Si₃N₄ with the same particle size,the Si₃N₄ content in the coating increases as the Si₃N₄ addition increases first.The hardness is mainly determined by the Si₃N₄ content of the coating.For Si₃N₄ with different particle sizes,Si₃N₄ content is 2g/L.For example,the Si₃N₄ content in the coating increases as the particle size increases,and the hardness decreases first.After the increase.The friction properties of Ni-W-P-Si₃N₄ composite coatings with different Si₃N₄ additions and particle sizes were compared and analyzed.The wear mechanism of composite coatings with different particle sizes was studied.The results show that the wear resistance of the composite coating is mainly related to the Si₃N₄ content of the coating at different addition amounts of the same particle size.For Si₃N₄ addition of 2 g/L,the wear resistance of the coating of different particle sizes is not only related to the hardness,but also The particle size is relevant.Three groups of loads and three groups of sliding speeds were selected to study the effects of load and sliding speed on the friction properties of Ni-W-P coating and Ni-W-P-Si₃N₄ composite coating.The results show that for the Ni-W-P coating,the average friction coefficient of the coating becomes larger with the increase of the load,and it first increases and then decreases with the increase of the sliding speed,and the change rule of the wear rate is the same;Ni-W-P-Si₃N₄ chemical composite coating,the frictioncoefficient increases with the increase of load and sliding speed,the difference is that the load has a significant impact on the friction coefficient,sliding speed has little effect on the friction coefficient.Orthogonal test method was used to study the effect of different activation liquids on the binding force between electroless plating and high-speed steel substrate.Orthogonal test results showed that hydrofluoric acid had the greatest impact on the binding force,followed by nitric acid and hydrochloric acid,followed by sulfuric acid;and the ratio of the activating fluid to obtain higher binding force was:hydrofluoric acid 5 ml,nitric acid 7.5 ml,15 ml of hydrochloric acid,15 ml of sulfuric acid,remaining distilled water.Drilling experiments for high-speed steel twist drill,Ni-W-P coated twist drill and Ni-W-P-Si₃N₄ composite coating twist drill are carried out.Under the same cutting conditions,the tool life of 40 Cr is compared.The results show that the wear resistance of Ni-W-P-Si₃N₄ composite coating and high speed steel tool has been greatly improved through life cutting test.