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Article

The Study of Thermal Stability of Mechanically Alloyed Al-5 wt.% TiO2 Composites with Cu and Stearic Acid Additives

by
Alexey Prosviryakov
* and
Andrey Bazlov
Department of Physical Metallurgy of Non-ferrous Metals, National University of Science and Technology “MISIS”, 119049 Moscow, Russia
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(2), 1104; https://doi.org/10.3390/app13021104
Submission received: 9 December 2022 / Revised: 8 January 2023 / Accepted: 12 January 2023 / Published: 13 January 2023
(This article belongs to the Special Issue Processing, Properties and Applications of Composite Materials)
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Abstract

:
In this work, we studied the effect of thermal exposure on the microstructure and mechanical properties of an Al-5 wt.% TiO2 composite material with additions of 5 wt.% Cu and 2 wt.% stearic acid as a process control agent (PCA), obtained by mechanical alloying. The composite was processed in a ball mill for 10 h. Composite granules were consolidated by hot pressing at 400 °C. SEM, XRD, and DSC analyses were used to study the microstructure, phase composition, and thermal behavior, respectively. Studies showed that the hot pressing of the material with copper addition leads to the precipitation of Al2Cu particles from the supersaturated solid solution and a decrease in the microhardness to 233 HV in comparison with the as-milled state (291 HV). In the material with a PCA additive, on the other hand, the microhardness increases from 162 to 187 HV due to the formation of aluminum carbide nanoparticles. In both cases, no reduction reaction products were found. At the same time, the Al-5TiO2-2PCA material after hot pressing shows a more stable grain structure than the Al-5TiO2-5Cu material. In addition, the compressive strength at 300 °C of the former material is 1.7 times higher than that of the latter one.

1. Introduction

Aluminum alloys are widely used in the automotive and aerospace industries due to their high specific strength and corrosion resistance. However, these alloys can no longer satisfy the growing requirements for new products. Therefore, aluminum-matrix composite materials reinforced with solid particles are becoming more widespread [1,2,3,4]. In the modern scientific world, the development of aluminum matrix composites is given the closest attention. Aluminum imparts some unique properties to composites, such as corrosion resistance, high specific and impact strength, high thermal and electrical conductivity, good wear resistance, and low density. It is well known that the mechanical properties of aluminum composites can be improved by introducing ceramic particles into a metal matrix. Aluminum matrix composites find various applications, including in the aerospace, military, and automotive industries, where high specific strength and good resistance to elevated temperatures are essential. Therefore, the development of aluminum matrix composites aiming to improve their physical and mechanical properties is important in modern science.
SiC [5,6,7], Al2O3 [7,8,9,10], TiB2 [11,12], B4C [13,14], TiC [15,16], and other ceramic phases with high hardness and melting point are used as conventional strengthening particles. Thus, titanium dioxide can also strengthen the aluminum matrix [17,18,19,20,21,22,23,24,25]. TiO2 occurs naturally in the mineral form of rutile, which is readily available, cheap, and has desirable mechanical and wear properties as well as corrosion resistance. The strengthening effect upon the introduction of solid particles into the metal matrix is achieved due to many factors, the main of which are grain refinement of the metal matrix (Hall-Petch effect) due to reinforcement particles, the load-bearing effect from the hard reinforcement phase by interfacial shear stress, and the Orowan strengthening effect caused by the resistance of closely spaced fine hard particles to the free movement of dislocations [1,26].
An important factor in the manufacture of dispersion-strengthened composites is the size of the strengthening particles. For example, it was shown [27] that the mechanical strength of aluminum composites could be increased by 20% if the size of the reinforcement particles was reduced from a micrometer to a nanometer scale. Various methods are used to obtain aluminum composites, such as ultrasonic casting [28], gas pressure infiltration [29], injection molding [30,31], semi-solid mechanical stirring [32], and mechanical alloying [33]. However, if liquid-phase methods are used for producing composite materials, the presence of contaminants on the particle surfaces hinders wetting by aluminum melt [34,35] which leads to a weakening of interface bonding and, as a result, a decrease in strength. In addition, when liquid phase processes are used, there is a difference in density between the matrix melt and the reinforcing particles, which prevents their even distribution. On the other hand, powder metallurgy methods deliver a significant increase in strength parameters [36,37,38].
An effective way to obtain dispersion-strengthened metal-matrix composites is the method of mechanical alloying (MA) related to powder metallurgy. This process avoids some disadvantages (e.g., segregation phenomena) typical of composites produced by liquid processes. When this phenomenon occurs, the distribution of alloy elements is not uniform, which may degrade the mechanical properties. On the other hand, the MA method can be used to obtain homogeneous nanocomposites due to the high degree of microstructure refinement. The essence of the MA technique lies in the processing of a metal powder together with one or more alloying components. In this process, composite granules are formed with a uniform composition and ultrafine microstructure due to complex physical processes. [39,40,41]. Hence, the method is unique because the process occurs entirely in the solid state. This method differs in that the powder components are not only homogeneously mixed but also significantly dispersed due to the severe plastic deformation accompanying the process. Severe plastic deformation leads to a dramatic increase in the density of crystalline defects. In this case, a homogeneous and, as a rule, nanocrystalline structure forms and is preserved at elevated temperatures [42,43,44]. The MA method can also be used to obtain supersaturated solid solutions [45,46,47] and amorphous materials [48,49,50].
The use of MA in the Al-TiO2 system contributes to the appearance of an energy stimulus to initiate a reduction reaction, which results in the formation of other hardening phases: Al2O3 and Al3Ti [51,52,53,54,55,56,57,58,59,60,61,62,63,64]. In general, a large number of works deal with the Al-TiO2 system. However, in the works that use the MA method, the microstructure and reduction reactions are mainly studied without attention to the mechanical properties of the prepared composites. Table 1 summarizes the data on the composition and mechanical properties of Al-TiO2 system composites obtained by different methods. As can be seen from Table 1, the use of MA to obtain an Al-TiO2 composite gives good results in strengthening the aluminum matrix. However, no studies have dealt with the effect of various additives on the microstructure and mechanical properties of composites or their stability as a result of thermal exposure.
In our previous work [65], we studied the effect of copper and stearic acid additives on the features of phase and structural transformations in the Al-5 wt.% TiO2 material as a result of heating during aluminum matrix melting. The aim of this work is to study for the first time the effect of these additives on the thermal stability of the microstructure and the mechanical properties of the mechanically alloyed Al-5 wt.% TiO2 material in the solid state.

2. Materials and Methods

The raw materials were powders of Al (purity of at least 99.0%) with a particle size of about 450 μm and rutile TiO2 (purity of at least 92.0%) with a particle size of about 1 μm. The content of TiO2 in the studied materials was 5 wt.%. Materials with two different compositions were studied. In one case, an additive of 5 wt.% Cu (purity not less than 99.5%) was used in the form of a powder for improving milling efficiency. The particle size was not more than 100 μm. In the other case an additive of stearic acid was used as a PCA in an amount of 2 wt.%. The powder mixtures were processed in a Retsch PM400 planetary ball mill at a rotation speed of 300 rpm in an argon atmosphere for 10 h. The ball-to-powder mass ratio was 10:1. Composite granules were compacted by initial cold pressing at room temperature and subsequent hot pressing at 400 °C. The compaction pressure was 500 MPa in both cases. The consolidated samples had a diameter of 6 mm and a height of 9 mm.
X-ray diffraction (XRD) analysis was carried out on a D8 Discover diffractometer (Bruker-AXS) in CuKα radiation. Primary processing of X-ray peaks and calculation of the centers of gravity with the integral widths were performed using the OUTSET software [66]. The microstructure was studied under a TESCAN VEGA 3LMH scanning electron microscope (SEM) with an XMAX-80 energy dispersive analyzer in the backscattered electron mode. Differential scanning calorimetry (DSC) was carried out on a SetaramLabsys 1600 calorimeter in an argon atmosphere with a heating rate of 20 K/min. An empty corundum crucible served as a reference sample. The microhardness was measured using the Vickers method on a 402MVD instrument at a load of 25–50 g. Compression tests were carried out with the use of a Zwick Z250 universal testing machine at room temperature and 300 °C. The machine’s crosshead rate was 4 mm/min. The nominal strain was calculated by dividing crosshead displacement by the initial sample height.

3. Results and Discussion

According to our previous study [65], the process of MA of Al-5TiO2 composites with additions of copper and stearic acid occurs in different ways. For example, the addition of 5 wt.% Cu contributes to the effective MA of aluminum with titanium oxide from the beginning of milling, while the addition of PCA postpones this process. The presence of stearic acid in the material during milling leads to the suppression of particle welding, which is necessary for the formation of composite granules. This is because stearic acid is adsorbed by the surface of the Al particles, resulting in a lubricating effect. For the material with the Cu addition, the welding stage develops intensively already after 1 h of milling. However, both processed materials reach the same steady state after 10 h.
Figure 1 shows images of granules of Al-5TiO2 composite materials with additions of stearic acid and copper obtained after 10 h of MA. In both cases, the formed particles have a uniform size and an equiaxial shape. The average particle size for the Al-5TiO2-2PCA material is about 140 µm, and for the Al-5TiO2-5Cu material, it is 100 µm. Thus, adding copper makes it possible to obtain a finer powder.
Figure 2 shows the DSC curves of the studied materials. Three exothermic peaks are visible on each of them, but their nature has some differences. To interpret them, we studied the microhardness of the cold-pressed powders as a function of the annealing temperature. The results are shown in Figure 3. For this study, the powders were compacted into tablets 10 mm in diameter and subjected to successive annealing at 200 to 500 °C with a holding time of 1 h at each temperature. Before measuring the microhardness, the tablets were carefully polished on sandpaper to a minimum fineness.
As can be seen from Figure 3, the microhardness of Al-5TiO2-5Cu granules after MA (291 HV) is significantly higher than that of Al-5TiO2-2PCA (162 HV), which is due to the effect of the solid-solution strengthening of aluminum by copper [67]. In addition, with an increase in the annealing temperature, starting at 200 °C, the microhardness of the material with the addition of PCA increases gradually, reaching a peak at 400 °C. With a subsequent increase in temperature, the microhardness decreases. The material with the addition of copper behaves somewhat differently. A decrease in its microhardness occurs after annealing at above 300 °C. Below this temperature, the microhardness of the material changes slightly.
The first peaks A and A’ in the range from 100 to 250 °C in both DSC curves are usually attributed to recovery processes when the concentration of point defects formed as a result of MA decreases [67]. However, for the copper-containing material, this peak should also be associated with the formation of Al2Cu dispersoids from a supersaturated aluminum solid solution formed during milling [68]. It is possible that the processes of recovery and aging are superimposed and therefore the microhardness changes only slightly up to 300 °C. The second peak B (250–400 °C) on the DSC curve for the material with the addition of PCA is probably associated with the formation of dispersed Al4C particles which is responsible for the increase in microhardness. The formation of aluminum carbide is caused by the appearance of carbon due to the decomposition of stearic acid during milling and subsequent heating and its reaction with aluminum [69]. The third peak C, which lies in the range from 400 to 500 °C, and the second peak B’ (380–480 °C) for the material with the addition of copper can be associated with grain growth (recrystallization) [67,70,71], which accounts for the decrease in the microhardness with increasing temperature for both materials (see Figure 3). Peak C’ (566 °C) belonging to the latter material is probably related to the reduction reaction starting in the solid state.
Figure 4 shows the XRD patterns of the studied materials after milling and hot pressing. It can be seen from this figure that there are two main phases in the materials: Al and TiO2, which indicate the absence of a chemical reduction reaction. In addition, the Al2Cu phase is present in the hot-pressed sample with the addition of copper (Figure 4b), its formation being confirmed by DSC data. The absence of the Al4C phase in the material with the addition of stearic acid should be associated with its dispersion and small amount. Figure 4 also shows that the Al peaks, both after milling and after hot pressing, are significantly broadened, which may indicate the nanocrystalline nature of the aluminum matrix.
A nanocrystalline structure is formed during MA as follows. At an early stage of MA, shear bands form due to high strain rates during MA [39]. These shear bands, which contain a high density of dislocations, have a typical width of about 0.5–1.0 mm. With further milling, the average deformation at an atomic level increases due to an increase in the dislocation density, and at a certain dislocation density in these highly stressed regions, the crystal breaks into subgrains separated by low-angle grain boundaries, causing a decrease in lattice deformation. During further processing, deformation occurs in shear bands located in previously undeformed parts of the material. The grain size decreases steadily, and the shear bands merge. Low-angle boundaries are replaced by high-angle grain boundaries, indicating grain rotation. As a result, dislocation-free nanocrystalline grains are formed. The minimum grain size achievable during milling is determined by the competition between plastic deformation due to the movement of dislocations and the behavior of the material during recovery and recrystallization.
Crystallite size and microstrain were estimated using the Williamson-Hall equation [72]:
β h k l cos θ = K λ D + 4 ε sin θ
where β is the integral broadening of the diffraction peak, θ is the Bragg angle, K is the shape factor (0.9), λ is the wavelength of Cukα radiation (0.154 nm), D is the mean crystallite size, and ε is the microstrain.
Plots based on the equation were drawn with 4 sinθ along the x-axis and βhklcosθ along the y-axis, as shown in Figure 5. These graphs make it possible to determine microstrain and crystallite size by the slope of the straight line and its intersection with the vertical axis, respectively. The microstructure parameters calculated for the aluminum matrix are shown in Table 2.
The following formula was used for the calculation of the dislocation density (ρ) [73]:
ρ = 2 3 ε D b
where b is the Burgers vector (0.286 nm).
The slope of the straight lines (Figure 5) for the materials, both after milling and after hot pressing, suggests that the dislocation density (Table 2) varies slightly depending on the composition and synthesis mode. The main difference in the graphs is that for the material with the addition of copper, the distance between the straight lines after milling and after hot pressing increases noticeably, as compared with that for the material with the addition of stearic acid. This fact is associated with a significant increase in the size of grains during hot pressing. Thus, the increment in the crystallite size of the Al-5TiO2-5Cu material is 32 nm, while for Al-5TiO2-2PCA it is only 23 nm (Table 2). In any case, the aluminum matrix remains nanocrystalline after hot pressing, which contributes to the preservation of the strength parameters. The grain boundaries are known to be effective barriers for moving dislocations that are blocked there, forming a pile-up [74]. Elastic stress fields arise around the pile-ups, which act on the boundaries and adjacent areas of neighboring grains in addition to external stresses. Under these conditions, new dislocation sources may form at the borders and in border areas. Accordingly, the finer the grains, the more boundaries/barriers are encountered in the path of gliding dislocations, and the greater the stresses required to continue plastic deformation even at its initial stages. As a result, more effective strengthening of grain boundaries is achieved.
It is interesting to note the change in the microhardness of the studied materials. Table 2 shows that for the material with copper addition, hot pressing leads to a decrease in the microhardness from 291 to 233 HV due to the precipitation of a stable Al2Cu phase from a supersaturated solid solution and grain growth during thermal impact. In this case, the decomposition of the solid solution is accompanied by an increase in the Al lattice parameter. However, for the material with a PCA additive, the microhardness increases from 162 to 187 HV after hot pressing despite a slight increase in the grain size. This effect may be due to the formation of dispersed particles of aluminum carbide, as noted above. A slight increase in the lattice parameter of this material after hot pressing is probably caused by the precipitation of impurity elements from the aluminum matrix.
The hardness of materials depends on their microstructure and the distribution of hardening particles. The microstructure of hot-pressed samples of the studied materials is shown in Figure 6. It can be seen that the microstructure of the materials in both compositions is homogeneous. The microstructure is a dark aluminum matrix with evenly distributed light particles not larger than 1 µm. However, in the material with the addition of copper, the amount of these particles is noticeably higher than in the material with the addition of PCA. This is because, whereas only TiO2 particles are visible in the Al-5TiO2-2PCA material, the Al-5TiO2-5Cu material, in addition to submicron TiO2 particles, also contains dispersed Al2Cu particles with a size of about 100 nm that precipitated from the supersaturated solid solution. Thus, the higher hardness of the material with the addition of copper is caused by a large number of hardening particles.
To confirm the formation of aluminum carbide particles (Al4C3) in the hot-pressed material with the addition of stearic acid, a fine microstructure study was carried out using TEM. Figure 7a shows that the material’s structure is nanocrystalline with a grain size of less than 100 nm, which confirms the X-ray diffraction data (Table 2). In addition, nanoparticles (shown by arrows) with a lamellar shape typical of the Al4C3 phase were found in the structure. Such nanorod-like particles were observed in mechanically alloyed materials if stearic acid was used as a PCA [69]. Moreover, the possibility of the formation of this phase was shown in our previous work [65].
The parameters of the microstructure affect the strength parameters not only at room temperature but also at elevated temperatures. The ability of the studied materials to withstand stresses at elevated temperatures was evaluated using compression tests at 300 °C. Compression diagrams are shown in Figure 8. It can be seen that the compression curve of the Al-5TiO2-2PCA material lies much higher than that for Al-5TiO2-5Cu. Thus, the yield and strength limits of the Al-5TiO2-2PCA material are 231 and 263 MPa, and for Al-5TiO2-5Cu143, and 153 MPa, respectively. That is, the strength of the former material is 1.7 times higher than that of the latter one, although the hardness of the material with the addition of stearic acid is, on the contrary, lower (Table 2). Annealing this material at 400 °C for 5 h decreases the strength parameters, yet they remain above 200 MPa. The high thermal stability of the material with the addition of PCA should be due to dispersed Al4C3 particles formed as a result of the decomposition of stearic acid.
The low thermal stability of the material with the addition of copper is associated with the low strengthening efficiency of Al2Cu stable phase dispersoids precipitating at the pressing temperature. In order to form reinforcing particles of metastable modifications typical of Al-Cu alloys, the hot-pressed Al-5TiO2-5Cu material was subjected to quenching and subsequent aging in conventional mode (540 °C, 5 h + 180 °C, 8 h). However, the strength indicators of the aged material with the addition of copper turned out to be even lower than those for the hot-pressed one. This is due to a significant coarsening of the grains due to exposure to a high quenching temperature, with the average grain size reaching 231 nm. Thus, the grain size contributes more to the strength at elevated temperatures than the size and shape of the Al2Cu dispersoids. Furthermore, the addition of stearic acid to the Al-5TiO2 material has a more significant positive effect on its thermal stability than the addition of copper.

4. Conclusions

In this work, we studied the effect of adding 5 wt.% Cu and 2 wt.% stearic acid on the thermal stability of the Al-5 wt.% TiO2 composite in the as-milled and hot-pressed (at 400 °C) states. It was shown that the hot pressing of the Al-5TiO2-5Cu material leads to the decomposition of the supersaturated solid solution and the precipitation of Al2Cu particles. In this case, the microhardness of the material decreases from 291 HV (in the as-milled state) to 233 HV. For the material with a PCA, on the other hand, the microhardness increases from 162 to 187 HV due to the formation of aluminum carbide nanoparticles. In both cases, no reduction reaction products were found. However, although both materials in the hot-pressed state retain the nanocrystalline structure formed by MA, the Al-5TiO2-2PCA material shows a smaller increase in grain size than the Al-5TiO2-5Cu material. In addition, compression tests at 300 °C showed that the strength as an indicator of the thermal resistance of the former material is 1.7 times higher than that of the latter material and is 263 MPa.

Author Contributions

Conceptualization, A.P.; methodology, A.P. and A.B.; software, A.P.; validation, A.P.; formal analysis, A.P.; investigation, A.P. and A.B.; resources, A.P.; data curation, A.P.; writing—original draft preparation, A.P.; writing—review and editing, A.P.; visualization, A.P.; supervision, A.P.; project administration, A.B.; funding acquisition, A.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was carried out with financial support from the Strategic Academic Leadership Program “Priority 2030”, project K2-2022-001.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors are grateful to V.V. Cheverikin and A.V. Pozdniakov for SEM studies, and to Yerzhena Zanaeva for editing the English.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 13 01104 g001 550
Figure 1. Morphology of composite granules containing (a) 2% stearic acid and (b) 5% Cu after 10 h of milling.
Figure 1. Morphology of composite granules containing (a) 2% stearic acid and (b) 5% Cu after 10 h of milling.
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Figure 2. DSC curves of composite powders with additions of (a) 2% stearic acid and (b) 5% Cu.
Figure 2. DSC curves of composite powders with additions of (a) 2% stearic acid and (b) 5% Cu.
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Figure 3. The effect of annealing temperature on the microhardness of cold-pressed powders.
Figure 3. The effect of annealing temperature on the microhardness of cold-pressed powders.
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Figure 4. XRD patterns of as-milled and hot-pressed composites with (a) 2% stearic acid and (b) 5% Cu.
Figure 4. XRD patterns of as-milled and hot-pressed composites with (a) 2% stearic acid and (b) 5% Cu.
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Figure 5. The Williamson-Hall plots for (a) Al-5TiO2-2PCA and (b) Al-5TiO2-5Cu composites.
Figure 5. The Williamson-Hall plots for (a) Al-5TiO2-2PCA and (b) Al-5TiO2-5Cu composites.
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Figure 6. SEM images of hot-pressed composites with additions of (a) 2% stearic acid and (b) 5% Cu.
Figure 6. SEM images of hot-pressed composites with additions of (a) 2% stearic acid and (b) 5% Cu.
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Figure 7. Bright-field TEM images of the hot-pressed sample with addition of 2% stearic acid: (a) nanocrystallite structure, and (b) lamellar nanoparticles of Al4C3.
Figure 7. Bright-field TEM images of the hot-pressed sample with addition of 2% stearic acid: (a) nanocrystallite structure, and (b) lamellar nanoparticles of Al4C3.
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Figure 8. Compression stress-strain curves of the hot-pressed materials in different states at 300 °C.
Figure 8. Compression stress-strain curves of the hot-pressed materials in different states at 300 °C.
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Table
Table 1. Composition, preparation methods, and mechanical properties of Al-TiO2 composites obtained in other works.
Table 1. Composition, preparation methods, and mechanical properties of Al-TiO2 composites obtained in other works.
Initial CompositionPreparation MethodFinal Phase
Composition		HardnessStrength
(Compressive/Tensile/Bending)		Ref.
AA7075–(5–30) vol.% TiO2MA + sinteringAl, TiO2, MgTiO3, ZnO100–168 HV—[18]
Al–(3–12) wt.% TiO2ball milling + sinteringAl, TiO286 HV (max.)σUCS = 158 MPa (max.)[19]
Al–15%SiC–(4–12) wt.% TiO2mixing + sinteringAl, TiO2, SiC45–75 HV—[20]
AA5051–(5–15) wt.% TiO2stir castingAl, TiO242–83 HBσUTS = 185–450 MPa[21]
AA6063–(6–18) vol.% TiO2friction stir processingAl, TiO280–142 HVσUTS = 250–325 MPa[23]
Al–16, 32 wt.% TiO2MA + sinteringAl, Al2O3, Al3Ti139 HV (max)σUCS = 375 MPa (max.)[51]
Al–10 wt.% TiO2mixing + sintering:
SPS
conventional
microwave		Al, TiO2
Al, Al3Ti, TiO2
Al, Al3Ti		134 HV
92 HV
234 HV		σUBS = 161 MPa
σUBS = 75 MPa
σUBS = 254 MPa		[25]
Table
Table 2. Microstructural parameters of the aluminum matrix obtained by XRD analysis and microhardness for different materials.
Table 2. Microstructural parameters of the aluminum matrix obtained by XRD analysis and microhardness for different materials.
Material/StateLattice
Parameter (nm)		Crystallite Size (nm)Microstrain (%)Dislocation Density (m−2)Microhardness (HV0.05)
Al-5TiO2-2PCA
as-milled		0.4047300.114.3∙10–14162 ± 4
hot-pressed0.4051530.163.5∙10–14187 ± 15
Al-5TiO2-5Cu
as-milled		0.4043280.197.9∙10–14291 ± 14
hot-pressed0.4049600.183.5∙10–14233 ± 22
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Prosviryakov, A.; Bazlov, A. The Study of Thermal Stability of Mechanically Alloyed Al-5 wt.% TiO2 Composites with Cu and Stearic Acid Additives. Appl. Sci. 2023, 13, 1104. https://doi.org/10.3390/app13021104

AMA Style

Prosviryakov A, Bazlov A. The Study of Thermal Stability of Mechanically Alloyed Al-5 wt.% TiO2 Composites with Cu and Stearic Acid Additives. Applied Sciences. 2023; 13(2):1104. https://doi.org/10.3390/app13021104

Chicago/Turabian Style

Prosviryakov, Alexey, and Andrey Bazlov. 2023. "The Study of Thermal Stability of Mechanically Alloyed Al-5 wt.% TiO2 Composites with Cu and Stearic Acid Additives" Applied Sciences 13, no. 2: 1104. https://doi.org/10.3390/app13021104

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