Experimental study on the interface stress of the

  • Detail

Experimental study on interface stress between tin coated ceramic tool film and substrate

1 introduction

tin film, as a kind of superhard coating, has high hardness, high wear resistance, low friction coefficient and good chemical stability, and has been widely used in tool and die coatings in machining. However, the adhesion between tin film and cemented carbide and ceramic tool matrix is poor, and it is easy to fall off from the matrix under the action of cutting force, which seriously affects the cutting performance and service life of tin coated tools. Therefore, how to improve the film substrate adhesion of tin coating has always been one of the research hotspots in this field. In this paper, the residual stress of tin film deposited on Si3N4 ceramic tool substrate was measured by X-ray diffraction sin2y method, the influence of residual stress on film substrate bonding force was studied, the morphology and composition of tin film substrate interface were measured and analyzed, and the mechanism of residual stress was preliminarily discussed. 2 test method sample preparation the sample adopts the commercially available Si3N4 ceramic forming tool, with the shape of a quadrangular prism and the size of 12.7mm × 12.7mm × 4.76mm. After quenching and stress relief annealing, the hardness is more than 65hrc. A tin film with a thickness of about 5 m is deposited on the ceramic tool substrate by PVD coating process. The test scheme uses x350a X-ray diffraction stress analyzer to conduct X-ray diffraction analysis on the tin film on the surface of the coated ceramic tool sample. The tube voltage is 22kv, the tube current is 6mA, the chromium target Ka characteristic radiation, the collimating tube diameter is 4mm, the stepped scanning step angle is 0.1 °, the time constant is 1s, the scanning start angle and end angle are 132 ° and 126 ° respectively, and the lateral inclination y is 0 °, 15 °, 25 ° and 45 ° respectively. For the Ka characteristic radiation of chromium target, the diffraction peak of tin film (311) crystal plane is selected for XRD linear analysis, and the X-ray absorption coefficient is taken as f= 2.5 × 105m-1, the matrix of the ceramic tool under the film is (22 2) crystal plane, and the diffraction angle is q=69.28 °. 3 experimental results and discussion theoretical analysis and calculation after Raman spectrum confirmed that the surface film of ceramic tool was tin phase, the stress of tin film was measured by X-ray diffraction. The measurement principle is: the existence of stress will cause lattice distortion and change the lattice constant. According to the Bragg diffraction formula (2dsinq=l), the crystal plane spacing of the film material can be determined, and the film stress is

(1) in the formula: e - it can prolong the shelf life of perishable foods such as bread by twice. The young's modulus of the film material s - Poisson's ratio d0 - crystal plane spacing e - film strain for tin films, e=450gpa, s ≈ 0.22, (22) d0=0.20592nm. The positive and negative of F correspond to tensile stress and compressive stress respectively. The intrinsic stress of tin film is obtained by subtracting the thermal stress value from the measured F value. Because the thermal expansion coefficient of tin film is different from that of ceramic matrix material, the X-ray diffraction results of high-performance fiber material industry in Shaoxing City, Xiaoshan District of Hangzhou city and Tongxiang City include the resulting thermal stress F1. The formula of F1 is

1-s (AF as)

(2) in the formula: e/(1-s) - biaxial Young's modulus of tin film, and the value is 1345gpa ET - thermal strain af - thermal expansion coefficient of tin film, af=(0.8~

4.8) × ℃ -1 as -- thermal expansion coefficient of matrix, as= (2.4 ~ 4.2) × ℃ -1 DT - the difference between the deposition temperature and the measurement temperature. Within the measurement range of this test, FT is a negative value, that is, the thermal stress is compressive stress. According to the equation fi=f-ft, the internal stress of tin film can be obtained from the measured total stress F and thermal stress ft. Structure analysis the mechanical properties of Si3N4 and tin are shown in Table 1. For tin-si3n4 system, the thermal expansion coefficient and elastic modulus of tin are greater than Si3N4. The microhardness of tin film measured by Knoop microhardness tester is 24GPa, especially in recent years

Table 1 Comparison of mechanical properties of Si3N4 and tin

coefficient of thermal expansion of material

(at this time, the mobile station should have no reaction k-1)

modulus of elasticity

(GPA) Poisson's specific density

(g/cm3) microhardness



3.25 ×

8.0 ×

20.5 analyze the microstructure of tin film and Si3N4 matrix with jsm-5800 scanning electron microscope (SEM) (see Figure 1); XRD texture patterns of SUS304 matrix and tin film were analyzed by X-ray diffraction (XRD) (see Figure 2); The composition of the film was determined by hitachis-530 (SEM) and linkisis spectrometer; The crystal structure and orientation of the films were determined by mxp18ahf diffractometer (XRD). The results showed that the films were polycrystalline; Auger electron spectroscopy (AES) was used to analyze the composition, and the contents of elements Ti and N were normalized. The results showed that the content of N atom in tin film was 48.80%, and its composition was close to the normal stoichiometric ratio

Copyright © 2011 JIN SHI