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30SHS BORON-CONTAINING LIGATURES, INTRODUCTION INTO THE MELT AND THE RESEARCH OF INFLUENCE ON THE PROPERTIES OF THE RESULTING ALUMINUM-MATRIX COMPOSITES
V. V. Sanin*", M. R. Filonov", Yu. A. Anikin", V. I. Yukhvidfi, and D. M. IkornikovA
aNational University of Science and Technology MISiS, Moscow, 119049 Russia bMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russia *e-mail: sanin@misis.ru
DOI: 10.24411/9999-0014A-2019-10147
Production of strong, durable, and thermally stable materials is one of the most important challenges of the today's metallurgy and material science. What makes aluminum matrix composite materials (AMC) so interesting is their unique properties, which combine low weight, high strength, high stiffness and modulus of elastic, low thermal expansion, and good wear resistance. This is what makes AMC promising and important materials that find use in many industries [1]. Of special interest are Al-based materials alloyed with boron and heavy metals (W, Mo) [1, 2]. Such alloying systems could feature a long-needed set of properties, including the structural properties of Al-based materials and radiation protection necessary for low-power nuclear plants used in aerospace, as well as for the space-based and terrestrial wireless electronics protections, which must feature specific weight and size.
The main challenge of making composites is to ensure the effective interaction of matrices and strengthening phases. In particular, direct injection of refractory particles (especially nanoscale ones) in an aluminum melt is nearly impossible due to their agglomeration and flotation caused by poor wettability in liquid metal. This challenge could be addressed by premade ligatures. Of importance is the way of synthesis of ligature, which helps optimize the phase composition of the strengthening phase particles.
To obtain ligatures of controlled phase composition, this research used self-propagating high-temperature synthesis. SHS can be used to make inorganic compounds of various classes (carbides, borides, nitrides, hydrides, silicides, oxides, intermetallics, and phosphides) as individual compounds or more complex ones [3]. With respect to light alloys, SHS ligatures consisting of individual crystallites of the target refractory phase are apparently feasible and promising. Agglomeration could be prevented by producing particles of refractory compounds separated with a thin matrix-alloy layer that melts while the ligature is being injected. Cast modified ligatures were synthesized (with a controlled alloying level and components) by front burning involving various active components injected directly into the source exothermic formulations. The burning of such formulations helps attain a temperature needed for melting the combustion products or producing cast synthesized ingots.
For this research, three boron-containing ligature systems were selected: (1) Co-B-Al, (2) Ni-B-Al, and (3) W-B-Al. Macrostructural analysis of the SHS-produced ingots for all the three systems revealed that defect-free ingots were formed at overloads above 30 to 40 g, depending on the system. Ingots synthesized at low overloads (below 30g) had gaseous (Fig. 1) and nonmetallic (aluminum oxide) inclusions, which was why ingots were further synthesized at ± 50g. Analysis of microstructure of SHS ingot confirmed the presence of all the target elements. Figure 2 shows SEM images of W-B-Al ligature; apparently, the target alloy has quite a dense structure without gaseous porous inclusions, which is important for the subsequent melting of the ligatures and Al by VIM. The morphology of the boride-phase (W2B5) particles is clearly faceted, which is typical of most boride materials.
(1g) (10g) (30g) (40g) (50g)
Fig. 1. Overall view of the cast samples of the W-B-Al ligature of the system after removal from the mold at different values of overload.
B, mass %
Al, mass %
W: mass %
15.80
15.86
68.34
(a) (b)
Fig. 2. (a) EDS data and (b) SEM images of the synthesized SHS-alloy modifying ligature for the W-B-Al system.
Injection of synthesized modifiers (SHS ligatures) in the aluminum melt was done in a Leybold-Heraeus vacuum furnace that can control the temperature and time of fusing. Pure aluminum (A99) was molten in vacuum as follows: heat to 700°C, cure for 5 min (during the 3rd minute, release Ar to 0.02 MPa), then inject a configured dose of the alloying formulation (SHS ligature) via a dispenser into the resulting melt.
Figure 3 presents the results of EDS analysis of melted AMC. Figure 3a demonstrates a zonal localization of higher Ni concentrations. Zonal inclusions have a mesh structure and are relatively uniformly distributed throughout the alloy. Unlike Ni, boron is distributed evenly regardless of the zonal Ni concentrations. Figure 3b shows that in the Al-Co-B alloying system, the post-fusing distribution is even for all the target elements, no zonal localization of boron or cobalt. EDS analysis data of the third system (Figure 3c) show that both tungsten and boron are evenly distributed throughout the alloy.
Al + (Al-Ni-B)
$$ v i- ■'; ^ '<*:$
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mr-r'M^/p- ^Wmv* h
¿v- . • v. ?/v..; • -, " . ' 1 fr : »î Z'<y I
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Al + (Al-Co-B)
Al + (Al-W-B)
B, Al. Ni, B, Al, Co, B, Al, W,
mass % mass % mass % mass % mass % mass % mass % mass % mass %
4.61 93.21 2.18 3.94 92.07 3.99 2.28 95.76 1.96
(a) (b) (c)
Fig. 3. EDS data of melted AMC.
Mechanical tests of cast rods of AMC modified with boron-containing alloying formulations were carried out (see Table 1).
Experimental data obtain for all the three systems during the reported study period represent the first positive experience of producing modified Al alloys by sequential combination of SHS (to synthesize cast boron-based ligatures) ensued by the injection of the synthesized alloying formulations during the VIM process.
Table 1. Mechanical properties of Al-Co-B, Al-Ni-B, and Al-W-B samples.
Sample Yield strength, MPa Maximum load, kN Tensile strength, MPa Relative extension, % Impact energy, J Impact strength, KCU, J/cm2 Hardness, HV
Al-Co-B 64.90 2.51 127.75 16.67 20.92 16.67 38.0
Al-Ni-B 45.76 1.93 98.19 33.33 74.70 33.33 42.0
Al-W-B 52.51 - 97.47 28.91 - 46 -
The reported study was funded by RFBR according to the research project
no. 18-38-00932.
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