Mechanical Behaviors Of Ti Metallization Films On Alumina Ceramic

Ceramic-metal joints are appropriate candidates for practical utilization in various fields,such as very-large-scale integration?VLSI?,micro-electromechanical systems?MEMS?and biomaterial industries.They perform excellently in severe environments owing to their comprehensive properties of both toughness,plasticity,electrical conductivity like metal and corrosion resistance,wear resistance,high temperature stability like ceramic.The reliability of joints highly depends on the wetting properties and coefficient of thermal expansion?CTE?between ceramic and metal.Pretreatment methods have been recently proposed to improve the interface wetting,among which the deposition of metallization films can provide advantageous pretreated surfaces.However,the wide application of this method is limited by the rigorous experimental conditions.Therefore,the present fabrication process and devices should be improved for practical utilization.Deformation and failure mechanism of metallization film materials are totally different from that of bulk materials,so it is necessary to make a full understanding of the mechanical behaviors under complicated conditions.Design and application of film materials and their composite structures are based on a detailed investigation on the plastic deformation model,energy dissipation and stress-strain relationship.Nano mechanical characterization methods are appropriate for materials and systems at micro or nano scale,especially for mechanical characterization of metallization films.In this paper,the effects of loading strain rate and penetration depth on film indentation size effect and creep were investigated by nanoindentation,and based on dimensional analysis the finite element analysis was employed to reversely obtain the elastic-plastic constitutive relation of metallization films.The research contents and results are as follows:1.Ti metallization films were fabricated on Al₂O₃ substrate by chemical vapor deposition method at different temperatures?1000°C,1050°C and 1100°C?with a specially designed reaction device.The results show that continuous metallized films with a thickness of?6?m were successfully obtained on Al₂O₃ ceramic substrate at all temperatures.Ti₂O?101?is the main phase in deposited film.Different surface and sectional topography can be detected in metallization films fabricated at different temperatures,among which film at 1050°C has the most uniform topography and the strongest film-substrate bonding without any caves or cracks.2.Nanoindentation test was conducted on films and load-displacement curves of specimens fabricated at different temperatures were obtained.At films deposited at 1000°C and 1100°C,micro cracks can be detected and the deformation mechanism is mostly elastic.However,at film deposited at 1050°C,there is no visible cracks and the deformation mechanism is mostly plastic.Film hardness and elastic modulus were obtained through Oliver-Pharr method.The values of film at 1050°C were the lowest,which is related to the microstructure.The scratch test was performed to determine the plastic deformation behaviors of metallized films.The results reveal that the critical load?L_c?can be sorted in the following sequence:1100°C<1000°C<1050°C.The wear test was conducted under continuous load to detect wear response.Both films deposited at 1000°C and 1050°C exhibit adhesive wear,while the film deposited at 1100°C exhibits typical abrasive wear.The wear resistance,plastic deformation resistance and crack formation resistance of films deposited at different temperatures were analyzed by hardness,elastic modulus and their combined parameters.Energy dissipation mechanism was discussed through scanning electron microscope.The results show that 1050°C is the optimal deposition temperature for Al₂O₃ ceramic metallization.3.The dimensionless functional relations between shape factor of load-displacement curve and elastoplastic mechanical parameters of film/substrate system were established via dimensional analysis.Unknown parameters shrank to only three by fixing three different indentation depths.For comparison,the loading work and unloading work were used to establish the equation set respectively.Based on the results of finite element analysis software ABAQUS,the effect of elastic modulus of ceramic substrate on the indentation process was detected to be small.Dimensionless functional relations were determined by fitting.Elastic modulus,yield strength and hardening parameter were obtained by reverse analysis combined with one indentation test.Reverse results were proved to be reasonable by using loading work,results using unloading work tended to induce errors due to uncertainty and unstable experimental environment.4.The Ti metallization films were investigated by nanoindentation through continuous stiffness method.Hardness and elastic modulus were analyzed via elastic contact theory and strain gradient plasticity theory.Indentation hardness increases at the beginning and then decreases.The initial inverse size effect is believed to be caused by tip passivation.Elastic contact between the passivated indenter and specimen leads to an increase of hardness.In addition,the experimental phenomenon is more compatible to theoretical value at low loading strain rate.Nix-Gao model was used to interpret the indentation size effect of hardness.As the loading strain rate increases,film hardness value and characteristic length increase.The elastic modulus exhibits the same trend as hardness.The phenomenon can be explained by the recovery resistance.5.Indentation creep test was conducted on Ti metallization films at different loading strain rates and different penetration depths.As the loading strain rate increases,the creep displacement tends to increase,but the creep stress exponent remains stable.Effect of penetration depths on creep behaviors is reflected at two phases.At the initial stage?maximum indentation depth<2000 nm?,as the penetration depth increases,the creep displacement increases and the creep stress exponent decreases.At the second stage?maximum indentation depth>2000 nm?,as the penetration depth increases,the creep displacement decreases and the creep stress exponent increases.