Strengthening Protective Boride Coatings with SHS-Produced Fe 2 Al 5
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Strengthening Protective Boride Coatings with SHS-Produced Fe2Al5 V. F. Aulova, *, Yu. N. Rozhkova, S. L. Silyakovb, **, and V. I. Yukhvidb, *** a
Federal Research Center VIM, Moscow, 109428 Russia Merzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected]
b
Received February 18, 2020; revised March 12, 2020; accepted March 18, 2020
Keywords: aluminothermic SHS, Fe2Al5, protective boride coating, cutting parts DOI: 10.3103/S1061386220030024
As is known, the technique of rapid induction boriding can be used for deposition of wear-resistant coatings onto cutting parts of soil-cultivating machines [1–3]. In order to further improve service parameters of thus deposited boride coatings onto spring steel 65G, we suggest their strengthening with
the Fe2Al5 intermetallic synthesized through aluminothermic Fe2O3–Al reaction. The details of our process for rapid MW-assisted deposition of wear-resistant coatings onto steel 65G can be found elsewhere [2, 3], while the experimental setup is presented in Fig. 1. In optimal conditions, the
(a)
(b)
Fig. 1. (a) Experimental setup and (b) still frames of the process.
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STRENGTHENING PROTECTIVE BORIDE COATINGS
c
I, rel. units
185
a
b
x x Fe2Al5
90 x
80
x
70 60
x
50
x
xx x
40 30 20
x x
x
10 100 μm 10 20 30 40 50 60 70 80 90 100 2θ, deg Fig. 2. Diffraction pattern of SHS-produced Fe2Al5 ingot.
sample temperature (as measured with an optical pyrometer) could reach a value of 1100–1350°С in 40–60 s and then be kept for 1–2 min until completion of the deposition process. Fe2Al5 intermetallic for use as a modifying agent was combustion-synthesized in air by the following reaction scheme: Fe2O3 + 7Al → Fe2Al5 + Al2O3 + Q. The diffraction pattern of as-prepared cast ingot is given in Fig. 2. The ingots were crushed down to powder with a particle size of 60–80 μm, and this powder was then added in an amount of 5 wt % to a standard boron paste used by us in rapid induction boriding [2, 3]. The resultant mixture was then used to deposit coatings as shown in Fig. 1. Combustion-synthesized Fe2Al5 and resultant boride coatings were characterized by XRD (DRON3.0 diffractometer, Cu Kα radiation) and optical metallography (Carl Zeiss Axio Observer.D1m apparatus). Microhardness Hμ was measured with a KMT-1 hardness meter. Chemical composition of deposited coatings (in wt %) is given below. It follows that the total amount of impurities in the material of coating is around 4.5 wt %. Fe
Al
Si Ni
Cr
Cu Mn
S
P
С
В
Fig. 3. SEM image of strengthened coating: (a) Fe2Al5 crystals, (b) ferrite-perlite crystals with dendrite inclusions (white), and (с) austenite interlayer.
Hμ, MPa Transition zone
Coating
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Steel 65G
100
80 1
2
60
40 ~ ~ 0
0.2
0.4
0.6
0.8 h, mm
Fig. 4. In-depth distribution of microhardness Hμ for (1) non-modified boride coating and (2) that modified with 5% Fe2Al5.
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