| 1. |
- Ahmadkhaniha, Donya, et al.
(author)
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The effect of co-deposition of sic sub-micron particles and heat treatment on wear behaviour of ni–p coatings
- 2021
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In: Coatings. - : MDPI. - 2079-6412. ; 11:2, s. 1-16
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Journal article (peer-reviewed)abstract
- The purpose of the study is to assess the influence of SiC particles and heat treatment on the wear behaviour of Ni–P coatings when in contact with a 100Cr6 steel. Addition of reinforcing particles and heat treatment are two common methods to increase Ni–P hardness. Ball-on-disc wear tests coupled with SEM investigations were used to compare as-plated and heat-treated coatings, both pure and composite ones, and to evaluate the wear mechanisms. In the as-plated coatings, the presence of SiC particles determined higher friction coefficient and wear rate than the pure Ni–P coatings, despite the limited increase in hardness, of about 15%. The effect of SiC particles was shown in combination with heat treatment. The maximum hardness in pure Ni–P coating was achieved by heating at 400◦C for 1 h while for composite coatings heating for 2 h at 360◦C was sufficient to obtain the maximum hardness. The difference between the friction coefficient of composite and pure coatings was disclosed by heating at 300◦C for 2 h. In other cases, the coefficient of friction (COF) stabilised at similar values. The wear mechanisms involved were mainly abrasion and tribo-oxidation, with the formation of lubricant Fe oxides produced at the counterpart.
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| 2. |
- Bogdanoff, Toni, et al.
(author)
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The complex interaction between microstructural features and crack evolution during cyclic testing in heat-treated Al–Si–Mg–Cu cast alloys
- 2021
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In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 825
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Journal article (peer-reviewed)abstract
- The study aimed to investigate crack initiation and propagation at the micro-scale in heat-treated Al–7Si–Mg cast alloys with different copper (Cu) contents. In-situ cyclic testing in a scanning electron microscope coupled with electron back-scattered diffraction and digital image correlation was used to evaluate the complex interaction between the crack path and the microstructural features. The three-nearest-neighbour distance of secondary particles was a new tool to describe the crack propagation in the alloys. The amount of Cu retained in the α-Al matrix after heat treatment increased with the Cu content in the alloy and enhanced the strength with a slight decrease in elongation. During cyclic testing, the two-dimensional (2D) crack path appeared with a mixed propagation, both trans- and inter-granular, regardless of the Cu content of the alloy. On fracture surfaces, multiple crack initiation points were detected along the thickness of the samples. The debonding of silicon (Si) particles took place during crack propagation in the Cu-free alloy, while cracking of Si particles and intermetallic phases occurred in the alloy with 3.2 wt% Cu. Three-dimensional tomography using focused ion beam revealed that the improved strength of the α-Al matrix changes the number of cracked particles ahead of the propagating crack with Cu concentration above 1.5 wt%.
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| 3. |
- Bogdanoff, Toni, et al.
(author)
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The influence of copper addition on crack initiation and propagation in an Al–Si–Mg alloy during cyclic testing
- 2020
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In: Materialia. - : Elsevier. - 2589-1529. ; 12
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Journal article (peer-reviewed)abstract
- The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt% to Al-Si-Mg alloys changes the fatigue behaviour that a rapid failure occurs.
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| 4. |
- Du, Andong, et al.
(author)
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On the efficient particle dispersion and transfer in the fabrication of SiC-particle-reinforced aluminum matrix composite
- 2023
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In: Crystals. - : MDPI. - 2073-4352. ; 13:12
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Journal article (peer-reviewed)abstract
- Lightweight SiC-particle-reinforced aluminum composites have the potential to replace cast iron in brake discs, especially for electric vehicles. This study investigates the effect of SiC particle size and matrix alloy composition on the resulting transfer efficiency and particle distribution. The performance of a specially designed stirring head was studied using a water model, and the stirring head conditions were assessed to understand the particle transfer and dispersion mechanisms in the molten aluminum. The standard practice of thermal pre-treatment promotes the wetting of the reinforcing particles and commonly causes clustering before the addition to the melt. This early clustering affects the transfer efficiency and particle dispersion, where their interaction with the melt top-surface oxide skin plays an important role. In addition, the transfer efficiency was linked to the particle size and the chemical composition of the matrix alloy. Smaller particles aggravated the degree of clustering, and the addition of rare earth elements as alloying elements in the matrix alloy affected the particle dispersion. The stirring parameters should be selected to ensure cluster disruption when the carbides are added to the melt.
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| 5. |
- Du, A., et al.
(author)
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On the hardness and elastic modulus of phases in SiC-reinforced Al composite : Role of La and Ce addition
- 2021
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In: Materials. - : MDPI. - 1996-1944. ; 14:21
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Journal article (peer-reviewed)abstract
- The use of silicon carbide particles (SiCp) as reinforcement in aluminium (Al)-based composites (Al/SiCp) can offer high hardness and high stiffness. The rare-earth elements like lanthanum (La) and cerium (Ce) and transition metals like nickel (Ni) and copper (Cu) were added into the matrix to form intermetallic phases; this is one way to improve the mechanical property of the composite at elevated temperatures. The α-Al15 (Fe,Mn)3 Si2, Al20 (La,Ce)Ti2, and Al11 (La,Ce)3, π-Al8 FeMg3 Si6 phases are formed. Nanoindentation was employed to measure the hardness and elastic modulus of the phases formed in the composite alloys. The rule of mixture was used to predict the modulus of the matrix alloys. The Halpin–Tsai model was applied to calculate the elastic modulus of the particle-reinforced composites. The transition metals (Ni and Cu) and rare-earth elements (La and Ce) determined a 5–15% increase of the elastic modulus of the matrix alloy. The SiC particles increased the elastic modulus of the matrix alloy by 10–15% in composite materials.
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| 6. |
- Du, A., et al.
(author)
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Role of matrix alloy, reinforcement size and fraction in the sliding wear behaviour of Al-SiCp MMCs against brake pad material
- 2023
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In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 530-531
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Journal article (peer-reviewed)abstract
- Aluminium metal matrix composites were produced by a newly developed stirring device for stir casting with different matrix alloys, SiC particle fractions and sizes to investigate these parameters' influence on the materials' wear performance. The wear performance of the composites was evaluated with dry sliding pin-on-plate tests against a high-speed train brake pad, and the study of wear surfaces was completed by electron microscopy. The formation of an iron-based tribolayer during wear protected the metal matrix composite from further wear damage. The composite reinforced with 19% SiC particles sized 32 μm showed an increasing coefficient of friction during wear, and the wear surface showed traces of third body wear. The rare earth and transition metal added to the matrix alloy increased the hardness of the composite, and the intermetallic phases reduced the development of the Fe-based tribolayer. The composites with small SiC particles presented the Fe transfer on the exposed aluminium surface, with a lower wear rate and friction coefficient than other composites. The direct comparison of composites produced with different sizes of SiC particles highlighted that the relationship between the wear rate and the coefficient of friction of the composites and the brake pad showed a linear trend.
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| 7. |
- Du, Andong, et al.
(author)
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The Influence of Ce, La, and SiC Particles Addition on the Formability of an Al-Si-Cu-Mg-Fe SiCp-MMC
- 2022
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In: Materials. - : MDPI. - 1996-1944. ; 15:11
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Journal article (peer-reviewed)abstract
- Road transport and the associated fuel consumption plays a primary role in emissions. Weight reduction is critical to reaching the targeted reduction of 34% in 2025. Weight reduction in moving parts, such as pistons and brake disc rotors, provide a high-impact route to achieve this goal. The current study aims to investigate the formability of Al–Si alloys reinforced with different fractions and different sizes of SiCp to create an efficient and lightweight Al-MMC brake disk. Lanthanum (La) and cerium (Ce) were added to strengthen the aluminium matrix alloy and to improve the capability of the Al-MMC brake discs to withstand elevated temperature conditions, such as more extended braking periods. La and Ce formed intermetallic phases that further strengthened the composite. The analysis showed the processability and thermal stability of the different material’s combinations: increased particle sizes and broader size range mixture supported the formation of the SiCp particle interactions, acting as an internal scaffolding. In conclusion, the additions of Ce and La strengthened the softer matrix regions and resulted in a doubled compression peak strength of the material without affecting the formability, as demonstrated by the processing maps.
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| 8. |
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| 9. |
- Lattanzi, Lucia, et al.
(author)
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Effect of Thermal Exposure Simulating Vapor Deposition on the Impact Behavior of Additively Manufactured AlSi10Mg Alloy
- 2022
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In: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 31, s. 2859-2869
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Journal article (peer-reviewed)abstract
- The present work focuses on the evolution of hardness and impact toughness after thermal exposure at high temperatures of the AlSi10Mg alloy produced by selective laser melting. The thermal exposure simulated the vapor deposition of coatings on aluminum alloys. The aim is to assess the possibility of combining the ageing step of heat treatments and the deposition treatment. The alloy was aged at 160 and 180 °C for up to 4 hours, both directly and after an innovative rapid solution treatment. Direct ageing had no significant effects on the microstructure, showing an almost constant hardness trend. These results accord with the impact properties, which showed a negligible difference in the impact toughness of the direct aged and the as-built samples. The same ageing treatments performed after rapid solution treatment induced age hardening in the alloy. The hardness values were lower by 38% than those of the directly aged samples. The innovative solution treatment positively affected impact toughness, which increased by 185% compared to the directly aged material. These results highlight that the ageing step can be integrated with the vapor deposition process. Moreover, the heat treatment is suitable for components requiring high impact strength after coating.
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| 10. |
- Lattanzi, Lucia, et al.
(author)
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Effects of microstructure and casting defects on the fatigue behavior of the high-pressure die-cast AlSi9Cu3(Fe) alloy
- 2017
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In: 3rd International Symposium on Fatigue Design and Material Defects (FDMD 2017). - : Elsevier. ; , s. 505-512
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Conference paper (peer-reviewed)abstract
- High-pressure die-cast (HPDC) components are being increasingly used due to good flexibility and high productivity. These aspects make HPDC suitable to produce several mass components, especially for the automotive sector. Due to the rapid filling of the die and high cooling rate, the process generally leads to the formation of a wide variety of defects, such as porosity and oxide films. Such defects might act as starting points for fatigue cracks and thus deteriorating the fatigue behavior of the casting. To this respect, the fatigue behavior of die cast aluminum alloys is an important aspect to consider when assessing the performance of complex castings for automotive applications. In the light of these aspects, the goal of this work is to describe how the microstructure affects the fatigue crack initiation and propagation. Die cast AlSi9Cu3(Fe) specimens were produced by means of a specifically designed die and the microstructure was preliminary characterized. Uniaxial fatigue tests were performed at load control with a stress ratio of R = 0.1 and at a single level of stress amplitude. After the fatigue tests, the samples were investigated to assess the propagation of the fatigue cracks; the starting points of cracks were specifically identified and the obtained data suggested how defects strongly influence the damage mechanism of the material.
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