宽固溶区过渡金属氮化物MN_x(M=Ti,Zr,Hf)硬质薄膜原子尺度强化机制研究

STUDY ON ATOMIC-SCALE STRENGTHENING MECHANISM OF TRANSITION-METAL NITRIDE MN_x(M=Ti, Zr, Hf) FILMS WITHIN WIDE COMPOSITION RANGES

采用增强磁过滤电弧离子镀技术在单晶Si基片上制备了3组不同过渡金属的氮化物薄膜MN_x(M=Ti,Zr,Hf).利用FESEM,GIXRD,XPS,Nano Indenter等方法对MNx薄膜的形貌、厚度、相结构、成分、元素的化学态、残余应力、弹性模量和硬度等进行了表征.结果表明,3组MNx薄膜均在较宽的成分范围内表现为fcc单相结构,并且同组薄膜间的择优取向、厚度、晶粒尺寸和残余应力等均基本保持一致;特别是3组薄膜的硬度和弹性模量均随N成分x的变化而变化,并且都在x=0.82附近出现性能峰值.分析表明,MNx薄膜与成分相关的性能增强,其决定性因素不在于介观尺度的晶粒细化、择优取向及内应力等,而是取决于原子尺度的化学键合及电子结构等因素.

Transition-metal nitrides have long attracted considerable attention among researchers and ubiqui- tous applications in various fields due to their renowned mechanical properties. However almost all the discussions of the strengthening mechanism were on conventional meso scale. For further understanding on the atomic scale strengthening mechanism of transition-metal nitrides, three groups ofMNx （M=Ti, Zr, Hf） films with different nitro- gen contents were synthesized on the Si substrates by magnetic filtering arc ion plating. The morphologies and thickness of the as-deposited films were characterized by FESEM, the microstructures and the residual stresses were characterized by XRD, the XPS and Nano Indenter were used to measure the chemical states and hardness （also the elastic modulus） of as-deposited films, respectively. The results show that all three groups MNx films per- form the Bl-NaCl single-phase structure within the large composition ranges. The preferred orientation, thickness, grain size and residual stress of the MNx films with different nitrogen contents were not changed so much. Whilethe nanohardness and elastic modulus of MNx both first increased and then decreased with the rise of nitrogen con- tent, and the peak values all existed when x near to 0.82. The strengthening mechanism was discussed and the deci- sive factor of composition dependent hardness enhancement was found from the atomic- scale chemical bonding states and electronic structure in this work, rather than the conventional meso-scale factors, such as preferred orien- tation, grain size and residual stress.