Effect of matrix on two-body abrasive wear of an Fe-B-Cr-C based alloy

Yanliang Yia*, Jiandong Xing a*, Yiming Gaoa, Hanguang Fub

aState Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi'an Jiaotong University, No.28, Xianning West Road, Xi'an, Shaanxi Province 710049, PR China

bResearch Institute of Advanced Materials Processing Technology, School of Materials Science and Engineering, Beijing University of Technology, Beijing100124, PR China

INTRODUCTION: To reduce the energy consumption, it’s imperative to design and apply green and new-style materials in daily equipment, especially for the wear-resistant materials acting as nonnegligible part [1-3]. Herein, the conventional wear-resistant materials taking carbide as hard phase will produce a lot of energy consumption, such as the Ni-hard cast iron and high chromium cast iron [4-7]. Recently, the high boron alloy taking boride as the hard phase attracts much commercially attention. Compared with carbide, the boride has higher hardness and heat stability [8-16], which can make Fe-B alloy become a kind of potential wear-resistant material.

In Fe-B alloy, the carbon almost dissolves in matrix while the boron exists at grain boundary in boride form. Thus, the appropriate ratio of matrix and boride can be controlled separately [8-10], which is a great breakthrough and can make it applied widely in wear- and corrosion-resistant materials [11-16]. Zhang [11] and Yi [12,13] had systematically investigated the abrasion resistance of Fe-B alloy, indicating that the Fe-B alloy could exhibit more excellent wear resistance than Cr15 white cast iron. Lv [14] showed that the Fe-3.08wt%B alloy presented high oxidation resistance owing to the formation of diffusion zone controlled by boron diffusion. Ma [15,16] presented that Fe2B with a skeleton microstructure could effectively resist liquid zinc corrosion. In addition, many boron-containing coatings were widely applied because of the excellent combination of hardness and toughness [17-20]. However, the hard phase Fe2B possesses inherent brittleness due to the weak B-B bond along [002] direction [21, 22], which leads to low plastic deformation ability and high susceptibility to cracking [23, 24]. That is, to inhibit the Fe2B from cracking, the Fe-B alloy should have high toughness and hardenability. So far, some researchers have attempted to improve the mechanical properties of Fe-B alloy. Jian [25-27] revealed that the appropriate Cr or Mn additions could improve the fracture toughness of the boride. However, excess Cr or Mn additions would lead to the increase of lattice distortion energy, reducing the fracture toughness of the boride on the contrary, as also reported in previous computational results [28,29]. Similarly, appropriate Cr or Mn additions could improve the hardenability of Fe-B alloy [11,30,31]. Moreover, Huang [32] and Chen [33] revealed that the appropriate Cr addition into Fe-B alloy could effectively affect the boride morphology, which could result in high wear resistance of Fe-B alloy. In addition, according to the previous works [10,15,34], the Cu or Ni atoms almost dissolved into matrix (i.e. Cu or Ni wouldn’t react with B), which would effectively improve the hardenability of Fe-B alloy.

Generally, during the abrasive wear process, the Fe2B will resist the abrasive and protect matrix from being shoveled off; in return, the matrix will support Fe2B against fracture. This synergistic effect can effectively improve the abrasion resistance of Fe-B alloy [11-13, 25-27]. Therefore, the effect of matrix on the abrasion resistance of Fe-B alloy is significant for its real application, while few investigations regarding this aspect have been reported. In present work, appropriate contents of Cr, Mn, Cu and Ni are added to improve the toughness and hardenability of Fe-B alloy. Then, the effects of matrix microstructure on the abrasion resistance of Fe-B alloy are discussed in detail.

 

METHODS: 

The wear samples were obtained by adding various content Cu and Ni into Fe-B alloy. Wear tests were performed on apparatus (ML-100 type pin-on-disk abrasion tester) with pin (ϕ 6 mm × 10 mm) against Al2O3 abrasive paper. The equipment and corresponding schematic representation were shown in Fig.1. Before the test, an initial stage of abrasion prediction was produced, using Al2O3 abrasive paper with 5N for a distance of 100 m to guarantee the same surface roughness for all samples. To avoid the degradation of the abrasive particles, the abrasive papers were changed after each test to guarantee that the specimens always encountered fresh triboenvironment. The pin abraded against the abrasive paper stuck to the disc in a spiral track. The parameters used were: rotating rate of 60 r·min-1, sliding rate of 4 mm·r-1, spiral orbit distance of 6 m and normal loads of 7N, 15N and 30N. The two-body wear tests were carried out under the same test conditions (i.e. only steady state wear was considered) to guarantee the test errors less than 5%. Each test was done at least three repetitions, and an

average weight loss and surface roughness were noted. To investigate the wear behavior, the morphologies of worn surface and cross-sections of wear samples were examined by using SEM and color 3D laser scanning microscope(VK-9710). After the wear test, the pin samples were prepared with the taper-section method to observe the morphologies of worn surface and subsurface [25-27]. Moreover, the pins after abrading were plated by nickel with about 50 um thickness, followed by cutting along vertical direction, and then the microstructure characterization of vertical sections against the worn surface was observed by SEM.

RESULTS: The abrasion resistance of Fe-B alloy is investigated as a function of the Vm/Vp, and an empirical relation is attempted to correlate the weight loss and surface roughness with the Vm/Vp as shown in Fig.1. Clearly, there’s sort of an approximate relationship between weight loss and Vm/Vp here: y=1.4553+1.5461exp (-0.4012x), and the Vm/Vp is related to the surface roughness with a relationship of y=1.666+0.58471exp (-0.5516x). It can be obviously seen that the weight loss and surface roughness decrease with the increase of Vm/Vp, especially for the stage of Vm/Vp less than 3.7. The specific reasons for this phenomenon are discussed in some detail hereinafter.


Figure 1  Wear weight loss and surface roughness as a function of the Vm/Vp under 7N normal load: (a) Weight loss; (b) Surface roughness.


DISCUSSION:

Under the constant contact stress, with the addition of Cu and Ni additions, the abrasion resistance of Fe-B alloy increases (especially for the stage of Vm/Vp exceeding 3.7 (where Vp and Vm show volume fraction of pearlite and martensite, respectively)), and the wear mechanism changes from microploughing to microcutting. The wear process can be described as follows: with the decrease of Vm/Vp or the increase of normal load, the neighboring M2B will be crushed by F⊥ owing to high degree of plastic deformation of matrix, and the broken M2B debris will be eradicated and dislodged by Al2O3 abrasive, so that the abrasion resistance of Fe-B alloy reduces greatly as a result. Accordingly, it was proven that the Fe-B alloy with martenste or high Vm/Vp matrix can be effectively subjected to severe abrasive wear in the low contact stress.

REFERENCES:

1.S. Aso, J. Jpn. I. Met. (1997), 2. A. Wiengmoon, Mater. Chem. Phys. (2011), 3. H.G. Fu, Mater. Sci. Eng. A (2007), 4. R.J. Chung, Wear. (2009), 5. C. Scandian, Wear. (2009), 6. R. Nieminen, Wear. (1994), 7. J. Liu, Wear. (1993), 8. C.Q. Guo, China. Foundry. (2008), 9. C.Q. Guo, J. Mater. Sci. (2004), 10. Y.L. Yi, Mater. Sci. Eng. A (2017), 11.  J.J. Zhang, Tribol. Lett. (2011), 12. D.W. Yi, Tribol. Lett. (2012), 13. D.W. Yi, Tribol. Lett. (2015), 14. Z. Lv, Corros. Sci. (2016), 15. S.Q. Ma, Corros. Sci. (2014), 16.S.Q. Ma, Acta. Mater. (2016), 17. H.G. Fu, J. Mater. Eng. Perform. 22(2013), 18.

J. Gu, Mater. Test. (2015), 19. S. Sen, Surf. Coat. Tech. (2005), 20. C. Martini, Wear. (2004), 21. O. Ozdemir, Vacuum. (2006), 22. M.S. Li, Acta. Metall. Sin. (1995), 23. S.Q. Ma, Corros. Sci. (2011), 24. O. Ozdemir, Vacuum. (2006), 25. Y.X. Jian, Tribol. Int. (2016), 26. Y.X. Jian, Tribol. Int. (2016), 27. Y.X. Jian, Wear. (2016)