The corrosion behavior and adhesion of ion-plated TiN film on AISI 304 steel

Transcription

1 The corrosion behavior and adhesion of ion-plated TiN film on AISI 304 steel Jia-Yang Chen, Ge-Ping Yu and Jia-Hong Huang Department of Engineering and System Science, National Tsing Hua University, Hsinchu,Taiwan, R.O.C. Abstract Titanium nitride was deposited on AISI 304 steel with a hollow cathode discharge (HCD) ion plating technique. An extensive investigation on the corrosion behavior and adhesion of TiN films was performed. The corrosion resistance was evaluated by the potentiodynamic polarization in 1N H 2 SO M KSCN solution and the ASTM standard B-117 salt spray test. The ultimate shear stress, proportional to the bonding strength between coating and substrate, was measured by a periodic cracking method to stand for the adhesion. To obtain good protection of the substrate, the Ti interlayer was introduced to form Ti/TiN multiple layers. The experimental results demonstrate that the corrosion properties of TiN-coated AISI 304 steel are determined first by the influence of the synergetic effect, that is the packing factor and thickness associated with the coating, and second by the adhesion of TiN coating. From the results of interfacial stress measurement and SIMS depth profiles, the adhesive strength of the coating increases with increasing the thickness of interdiffusion layer. Furthermore, it also indicates that the Ti sublayer can enlarge the pseudo-diffusion layer and enhance the adhesion strength of TiN coatings. For Ti/TiN Multilayered coating, good corrosion resistance can be obtained with the measured ultimate shear stress higher than 10GPa and the interdiffusion zone higher than 0.2 μm. 製作 : 管維仁

2 Experimental Procedure Taguchi Experimental Design One Variable Experiment Properties Corrosion Test Structure Salt Spray Potentiodynamic Microhardnes Ultimate Shear Stress Measurement Polarization XRD SIMS ESCA Experimental Results The results of ultimate shear stress test and electrochemical test for TiN single layer coatings TiN τ uss I corr I critical Salt Sample thickness Packing Spray ID (μm) factor (GPa) (na/cm 2 ) (μa/cm 2 ) Test 304SS S F (1) S F S F S F S F S P (2) S F S P S P S F S P S P S F S F S P S P The results of ultimate shear stress test and electrochemical test for Ti/TiN multilayered coatings Ti - TiN Interdiffusion zone τ uss I corr I critical Sample Thickness Thickness Packing ID (μm) (μm) factor (GPa) (na/cm 2 ) (μa/cm 2 ) T T T T T T T *All the specimen listed above were doposited at Ts=350 and I=200 A. Note: (1) F= failed the test, as evidenced by locallized surface attack (2) P= passed the test

3 The morphology of TiN coating after electrochemical test The surface of the attacked TiN-coated steel after a 500 hours salt spray test

4 10 7 Secondary Ion C ounts Fe C r O N 10 1 Ti C D epth ( µ m ) Composition depth profile of Ti/TiN sample T6 by SIMS The composition depth profile corrosion current density (na/cm 2 ) (Thickness of TiN ) * (Packing factor) The corrosion current density VS. [thickness of TiN] [packing factor ] plot in 1N H2SO M KSCN solution. The effect of packing factor and thickness on the corrosion resistance

5 10 5 Critical current density ( µa/cm 2 ) ( Thickness of TiN )*( Packing factor ) The critical current density VS. [thickness of TiN] [packing factor ] plot in 1N H 2 SO M KSCN solution. 1.0 : Corrosion : Immunity Packing factor Thickness of TiN ( µm ) The effects of packing factor and thickness of TiN coatings resulting from the outcomes of salt spray The effect of Ti interlayer

6 10 4 Critical current density ( µa/cm 2 ) =0.5 mtorr =1.0 mtorr =1.5 mtorr =2.0 mtorr with Ti interlayer Ultimate shear stress ( GPa ) The illustrations showing the effects of ultimate shear stress to Corrosion. 350 Critical current density µa/cm ( 2 ) Thickness of pseudo-diffusion layer (µm ) The effect of thickness of interdiffusion layer to the critical current density showing the influence of adhesion on corrosion behavior.

7 Conclusions The corrosion behavior of TiN-coated stainless steel is controlled by two factors: one is the synergetic effect of [ packing factor ] [ thickness of TiN ], which is related to the structure of hard coating, and another is the interfacial stress, which related to the adhesion of TiN coating. The corrosion happens because of the defects in structure, and it is aggravated by the poor adhesion strength of TiN coatings. The Ti interlayer not only provides better protection for corrosion but also enhances the bonding of the TiN/substrate interface. The interdiffusion zone broadens with the Ti interlayer and overlaps the Ti interlayer in some extent, and it also helps to increase the adhesion of TiN. For corrosion protection, the interdiffusion depth is proper about 0.2μm and the packing factor should be higher than 0.8.