Interfacial structure and mechanical properties of surface iron–nickel alloying layer in pure iron fabricated by surface mechanical attrition alloy treatment
Highlights
► A refined Fe/Ni alloy surface layer about 50 μm was fabricated by SMAAT. ► The SMAAT process includes impacting, grain refinement and synchronous diffusion. ► The reduced diffusion activation energy accelerates short-range diffusion. ► The intermetallic/alloy phases have been formed during SMAAT. ► Refine and alloy reduce fatigue wear effect and improve friction and wear properties.
Introduction
Bulk metal materials surface nanocrystallization technique provides an important method to modify the physical, chemical and mechanical properties of a surface, which can be one of the more effective ways to substantially improve the overall behavior of a component. Surface mechanical attrition treatment (SMAT), as an effective surface nanocrystallization approach, has been developed to fabricate a plastic deformation surface layer with the gradient distribution of grain sizes along the deformation depth and with a certain depth of nanometer grains in the upper surface [1], which can effectively enhance the surface service properties. SMAT has been successfully applied in many material systems, including but not limited to pure iron [1], pure copper and titanium [2], Ti6Al4V [3], [4], Fe–Ni alloy [5], [6], Fe–23.4Mn–6.5Si–5.1Cr (wt.%) [7], magnesium alloy [8], [9] low carbon steel [10] and stainless steel [11]. The interfacial structure and mechanical properties of the SMATed nanocrystalline surface layer have been reported, the mechanics of refinement of coarse grains from the micrometer to nanometer scale has been understood fully and the intrinsic principle of the property transformation of surface nanocrystallization has been mastered basically [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Such as the treated surface becomes chemically active, which promotes the effectiveness of subsequent treatments such as chromizing [1], [10], nitriding [12] and ion implantation [13].
Research into the SMAT process has led to the observation that some scrapings fell off from the peening ball and target plate owing to fatigue effect after lengthy impact treatment. These scrapings could be re-enchased into the specimen surface during the latter process. These findings suggest that foreign elements can permeate into the treated surface by severe plastic deformation over the course of the SMAT process. Based on these physical phenomena, the author has brought forward the theme of the surface mechanical attrition alloy treatment (SMAAT) [14], [15]: The aim of SMAAT is to introduce metal or alloy powders into the container, bring them to the deformed surface by SMAT and produce a surface alloy layer in the target plate specimen. It is obvious that SMAAT is a new important application of surface modification based on SMAT. For further development of the SMAAT technique, a clear understanding of the interfacial structure and mechanical properties of the alloy layer is necessary.
In this work, pure iron was selected for SMAAT, hardened GCr15steel balls and Ni powders were added to the sample container. After SMAAT and subsequent low temperature annealing heat treatment, a refined Fe/Ni alloy surface layer was fabricated onto the iron surface. Microstructural characterization and morphology of the alloy surface layer before and after heat treatment were investigated contrastively by means of optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Micro-hardness and the friction and wear behavior of alloy surface layers were studied in comparison with those of the SMATed-only nanocrystallization counterpart. The worn surfaces were studied using the OM equipped with a CCD camera.
Section snippets
Experimental work
The preparation of experimental materials, SMAAT apparatus and processing are identical to those described in Ref. [15]. In brief, commercial pure iron plates (100 mm × 100 mm × 3 mm in size) with a purity of 99.95 wt.% and commercial Ni powders (particle size of −200 meshes) were used in this work. The iron sample was annealed at 950 °C for 2 h in vacuum to eliminate the effect of mechanical deformation and to obtain homogeneous coarse grains with an average grain size of 100–150 μm. The hardened GCr15
Results and discussion
Fig. 1 shows the SEM observations of the sample surfaces after SMAAT with and without annealing treatment. It can be seen that the un-annealed sample surface (Fig. 1a) has been equably welded with Ni powders. The surface appears to be very coarse and loose, and looks like the colloidal mud has been beaten repeatedly for a long time and got into a toughened state.
In fact, in the course of the SMAT process [1], [5], [7], [8], [9], [10], [11], because of the high vibration frequency of the system,
Conclusions
In this paper, the interfacial structure and mechanical properties of surface iron-nickel alloying layer in pure iron fabricated by surface mechanical attrition alloy treatment was studied. The following conclusions can be obtained:
- (1)
The SMAAT process includes impacting with high strain velocity, grain refinement and synchronous diffusion. By means of SMAAT with Ni powders and followed by annealing treatment at 450 °C, a layer of refined Fe/Ni alloy surface layer with the depth of about 50 μm was
Acknowledgments
The authors gratefully acknowledge gratitude to the National Natural Science Foundation (51001079, 50471070), PR China, the Science and Technology Project of Shanxi Province (20090321072), Ph.D. Programs Foundation of Ministry of Education of China, Shanxi Province Foundation for Returned Scholars, the Shanxi Province Young Science Foundation (2010021023-1), Foundation for funding and Innovation for undergraduate of Taiyuan City (01922034) financial support to this work.
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2019, Materials Science and Engineering: ACitation Excerpt :The SMAT technique had been used to fabricate nano-crystalline-surface layers on many kinds of metals or alloy materials [4]. The industrial pure iron [5–13], low carbon steel [14–18], stainless steel [19–24], hardening steel [25],Ti [26–28], Al alloy [29,30], Cu [31–34], Mg alloy [35–38], eutectoid steel [39], tungsten alloy [40], Fe-Ni alloy [41], Co [42,43], CuCr Alloy [44], Ni3Al [45,46], Inconel600 [47], amorphous [48,49], GW103K alloy [50], NiTi shape memory alloy [51,52], and Ni base C-2000 super alloy [53–59] are included in the study of surface nano-crystallization. The simulation is an effective method to study the fabrication process or properties of materials, by which severe shot peening has been studied [2,60,61].