Preparation And Properties Of Super-hard Amorphous Al-Mg-B Thin Films

With the rapid development of modern manufacturing industry, higher properties are requested for cutting tools, grinding tools and wear parts, such as the higher hardness, the better wearing resistance, the longer service life. Therefore, super-hard materials are gradually developed to achieve low density, low friction coefficient, low cost et al. Due to the boride material possesses excellent hardness and wearing resistance, it shows excellent performance as the production of cutting tools and grinding tools. Consequently, the research and development of super-hard boride material have attracted much attention.In boride material, ternary metal boride AlMgB14has beed widely investigated due to its advantages of high hardness and low friction coefficient. Bulk crystalline materials prepared by high-temperature sintering of powder are generally used in previous investigation. However, in practical application, the thin film material plays an important role in the national economy in many fields. This is because the thin films can be attached to the surface of the complex tools by using fewer amounts and consequently endued the substrate material with new properties. On the other hand, due to the characteristics of high strength, high toughness and strong corrosion resistance of the amorphous materials, it has the good performance in many complex and harsh work environment. Therefore, amorphous Al-Mg-B thin film can further improve the performance, and promote the research and development of ternary metal boride (XYB14). However, the study of deposition process and hardening mechanism is still lack, which constrains performance optimization of the amorphous Al-Mg-B thin film materials and further development and application.To address this problem, in this present work, the magnetron sputtering technology and multi-target sputtering scheme are employed to prepare amorphous Al-Mg-B thin films. The process parameters, including the sputtering power, deposition temperature, deposition pressure and negative bias, were optimized. The critical proress parameters which could affect the film properties were analyzed. It was found out that the hardness of the films increases at first and then decrease with the increase in boron sputtering power but the surface roughness and friction coefficient of the film decreased gradually; the hardness of the film increased and the friction coefficient decreased with the increase in deposition temperature and deposition pressure; the hardness of films increased firstly and then decreased with the increase in negative bias. In the case of composition optimization, the highest hardness37.1GPa appeares at a composition of boron93.1at.%, while the friction coefficient was only0.15. On the other hand, amorphous Al-Mg-B thin film with a similar composition as that of crystalline AlMgB]4material has a comparative hardness comparing with crystal AlMgB14material (28GPa), the nano-hardness was31.1GPa. Moreover, the optimized deposition conditions corresponding to this film are deposition temperature600℃, deposition pressure0.9Pa. and negative bias voltage80V.Based on these results, high performance Al-Mg-B amorphous films were deposited on the surface of YG6X cemented carbide cutting tools by applying these optimized deposition conditions. The film shows relatively high bond strength with the YG6X alloy. The hardness of YG6X was44.6GPa and the friction coefficients was0.11. Moreover, he coated cutting tool shows better cutting performance.According to the deposition and characterization results, the hardening mechanism of Al-Mg-B amorphous film was analyzed. It was suggested that the short-range orderd Bl2icosahedron structure in the crystalline materials was reserved in the amorphous film, and the existence of this structure dominantes the hardness of the amorphous film. This suggestion was first demonstrated by first principle simulation of the hardness of AlMgB14and a-B. The determinant effect of B12icosahedron structure on the hardness was elucidated by electronic structure simulation. Then, the Al-Mg-B amorphous films were doped by four different elements. It was found out that the amorphous Al-Mg-B films doped by Ti and Si still have a high hardness, and B12icosahedron still exists with a steady state. However, the doping of Cr and N blocked or damaged the formation and existence of B12icosahedron, and. hence, the mechanical performance of Al-Mg-B films was decreased. This result further confirms the role of B12icosahedron structure in the high hardness of Al-Mg-B amorphous films.According to the effect of B12icosahedron structure on the high hardness of Al-Mg-B amorphous films, elements that can stabilized the B12icosahedron structure can be selected by doping. Then, a [cluster](connecting atoms) model can be used for developing new metal borides materials with high performance.The results of this work provide a reference of deposition proress for industrial manufacture of coated cutting tools. Moreover, they can promote the development of new metal borides materials with high performance.