Microstructure And Properties Of (AlTiZrVHf)N High-entropy Alloy Nitride Films

Mold is an indispensable part in the mechanical manufacturing field,such as Cr12Mo V die steel.However,due to its low hardness,the wear amount increases and the service life decreases.It is difficult to effectively solve the problem about insufficient hardness of Cr12Mo V die steel,only by single component allocation and existing film system.High-entropy alloy films have attracted extensive attention of scholars at home and abroad because of their excellent comprehensive properties.In this paper,a novel AlTiZrVHf high entropy alloy was designed and the AlTiZrVHf thin films were prepared by reactive magnetron sputtering.The optimum process parameters of(AlTiZrVHf)N thin films were obtained by orthogonal experiment.The evolution laws of substrate temperature and target sputtering power on the microstructure and properties of the film were systematically studied.The hardness of the film was significantly improved by introducing B element,the effect of B element content on the microstructure and properties of the film was systematically studied,and the wear properties under different loads and rotational speeds were studied on the basis of the best hardness.The specific research results are as follows:Through thermodynamic parameters simulation calculation,both the AlTiZrVHf target and film are BCC structures.The experimental results are consistent with the calculated phase structure,but the hardness of the film is 2.97 times that of the target.The substantial hardness increase is attributed to nano-particles and related nano strengthening effect via magnetron sputtering.The optimum parameters for(AlTiZrVHf)N thin films were obtained by orthogonal tests:the substrate temperature was 400°C,the sputtering power of the target was 180W,the substrate bias was 250V,and the nitrogen flow rate ratio is 37.5%,the hardness and elastic modulus of the films prepared were the largest,47.64 GPa and 318.36 GPa,respectively.Substrate temperature has the most significant effect on the film hardness,followed by sputtering power,substrate bias and nitrogen flow rate ratio.The(AlTiZrVHf)N thin films prepared at different substrate temperatures and sputtering powers were mainly composed of FCC+BCC dual-phase structure and with preferential growth on the(111)crystal plane.Besides,the particle size of the films had gradually increased.The surface was smooth and flat with a small amount of cluster particles,nitrogen contents is close to50at.%,and the hardness and elastic modulus of the film firstly increased and decreased.When temperature increased from 25°C to 450°C,the film deposition rate decreased from 5.22 nm/min to 4.70 nm/min.The main reason is that the desorption capacity of the thin film deposited particles increased with the increase of substrate temperature.When sputtering power increased from170W to 200W,the film deposition rate increased from 5.16nm/min to 5.63nm/min.The main reason is that the number of particles deposited in film increased with increasing sputtering power.Adding B element further improves the hardness and elastic modulus of(AlTiZrVHf)N film,When the content of B is 17.13 at.%,the film hardness and elastic modulus are maximal,51.42 GPa and 359.33 GPa,respectively.Each element exists in the form of c-BN,Ti N,Zr N,VN hard phase,Al,Hf and a small amount of oxides in the film;with the continuous increasing of load,the wear mechanism of(B_17.13AlTiZrVHf)N film changes from single abrasive wear to abrasive wear and adhesive wear.The wear mechanisms of(B_17.13AlTiZrVHf)N films at different rotating speeds is abrasive wear;the wear resistance of(B_17.13AlTiZrVHf)N film with different load and speed is better than that of Cr12Mo V substrate.It is the main candidate material for die coating and can be extended to the field of tool coating.