The microstructures of subsurface layers of 20CrMnTi steel pins against chroming and nonchroming T10 under dry sliding tests were studied by means of OM (optical microscopy), XRD (X-ray diffraction), and SEM (scanning electron microscopy). Results showed that the chroming coating strengthened the disc surface and significantly affected microstructural evolution. Three layers—the matrix, deformation layer (DL), and surface layer (SL)—formed in 20CrMnTi for the chroming T10. The matrix and deformation layer (DL) formed in 20CrMnTi for the nonchroming T10. The formation of the microstructure was considered as a result of the shear deformation.
Chroming is an interesting and intriguing coating technology. How the chroming coatings protect the substrate material interests both materials academic and technological communities [
The microstructure evolution of ferrous alloy surface layer studied in [
Our group has concentrated on improving surface properties of the T10 tool steel using the surface chroming coatings, which can satisfy the requirements of machining operation. The focus in this manuscript is to systematically investigate the microstructural evolution in advanced structural carbon steel friction pairs with and without chroming coatings under dry sliding testing conditions.
The 20CrMnTi steel contains 0.2% C, 1.2% Cr, 0.1% Ti, 0.95% Mn, and Fe balance, and the T10 steel contains 0.98% C and Fe balance. The original 20CrMnTi steel pins have hardness of about 200 HB (
Friction and wear behaviors of chroming and nonchroming T10 steel discs were evaluated by laboratory tests, which were performed on the MM-W1 friction testing machine. All experiments were taken with a speed of 0.3 m/s, with load of 60 N, for 2 hours, and at 300 K. Friction coefficients were recorded online in a computer during the test.
The chroming coating of T10 was observed with a Nikon optical microscope. The constituents were detected with a MAX2550V X-ray diffractometer (XRD).
Wear scars and the cross-section microstructures of chroming and nonchroming T10 discs and the worn surface layers of 20CrMiTi pins after the dry sliding test were observed by a HITACHI S-570 scanning electron microscope.
A microhardness tester (MH-3) was used to measure the microhardness distribution across the cross-section of 20CrMnTi pins against the chroming and nonchroming T10 steel discs using a Vickers indenter under a load of HV0.01 with a dwell time of 20 s.
The coating sectional area OM image is shown in Figure
(a) OM micrograph of chroming layer; (b) XRD spectra of chroming coatings.
Figure
Figure
The friction coefficients versus friction time for chroming and nonchroming coated T10 steel discs against 20CrMnTi steel pins were illustrated in Figure
Wear loss and wear rate of chroming/nonchroming T10 discs against 20CrMnTi pin.
Mass losses (g) | Wear rate (g/m) | |
---|---|---|
Chroming T10 disc/20CrMnTi pin | 10.63 × 10−3/46.28 × 10−3 | 4.92 × 10−6/21.43 × 10−6 |
Nonchroming T10 disc/20CrMnTi pin | 16.72 × 10−3/23.68 × 10−3 | 7.74 × 10−6/10.96 × 10−6 |
Friction coefficient versus friction time for the nonchroming and chroming friction pairs.
Wear-scar morphologies of the chroming and nonchroming T10 steel discs against 20CrMnTi pins after dry friction test are shown in Figure
Wear scars of (a) chroming and (b) nonchroming T10 discs after dry sliding.
Wear scars of (a) 20CrMnTi pins against chroming T10 disc and (b) 20CrMnTi pins against nonchroming T10 disc after dry sliding.
The SEM cross-section micrographs of the chroming and nonchroming T10 discs against 20CrMnTi steel pins after dry sliding are shown in Figure
SEM cross-section micrographs of the (a) chroming and (b) nonchroming T10 discs.
Figure
SEM images of the worn subsurface layers of 20CrMnTi pins against the (a) chroming and (b) nonchroming T10 discs.
Figure
Note that Figure
Thus, the chroming layer made its counterpart go through more severe and deeper plastic deformation than the nonchroming one. In other words, the chroming layer might protect its matrix materials much better than the nonchroming one.
For the 20CrMnTi against the chroming T10 in Figure
Microhardness profiles of 20CrMnTi pins against (a) chroming and (b) nonchroming T10 discs as a function of the depth beneath worn surface.
For the 20CrMnTi against the nonchroming T10 in Figure
According to the above experimental results, the chroming and nonchroming T10 discs have different hardness and microstructures. Thus, they present different wear mechanisms for the 20CrMnTi steel pins. The wear mechanism of the chroming T10 steel disc is mild oxidation wear [
In contrast, the wear mechanism of the nonchroming T10 steel disc is delamination wear, owing to plastic deformation [
The 20CrMiTi pin against nonchroming T10 disc would be more softened and worn than the pin against the chroming friction pair [
Furthermore, the chroming T10 protected its matrix materials from being seriously damaged, and only some microcracks occurred in the chroming layer without endangering the substrate material (Figure
The mechanism of the outstanding wear resistance in the chroming T10 steel discs is considered to be the formation in the 20CrMnTi pin, which helped them undergo less severe shear deformation than the nonchroming friction pair.
The microstructures of subsurface layers of 20CrMnTi against chroming and nonchroming T10 under dry sliding tests were observed. Some conclusions were drawn: The friction coefficient of chroming friction coefficient is considered, and the antifriction properties of chrome-plating layer have a strong influence on the surface chroming layer. Three layers, which corresponded to matrix, DL, and SL, were observed beneath the worn surface in the 20CrMnTi against the chroming T10. Matrix and DL were observed in the 20CrMnTi against the nonchroming T10. The mechanism of the outstanding wear resistance in the chroming friction pair is considered to be the formation of the SFIDL in the 20CrMnTi. The SFIDL help them undergo less severe shear deformation than the nonchroming friction pair.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The present work was supported by the National Natural Science Foundation of China (Grant no. 11372226), the Outstanding Young Teachers’ Special Funding of Shanghai Municipal Education Commission (ZZSDJ14007), the Scientific Research Innovation Project of Shanghai Municipal Education Commission (15ZZ104), and the Science and Technology Sail Plan of Shanghai Science and Technology Commission (15YF1404400).