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Kinetics of Laser Surface Engineering of Three Aluminum Alloys
Published in T. S. Srivatsan, T. S. Sudarshan, K. Manigandan, Manufacturing Techniques for Materials, 2018
Sourabh Biswas, Sandip P. Harimkar
The traditional laser composite surfacing, as discussed, involves injecting hard particles to the laser melt pool. Other novel approaches have also been attempted to develop in situ composites at the surface using laser irradiation, as in situ composites often exhibit superior bonding strength between the matrix and particles. An approach for developing in situ metal matrix composite coating on 2024 alloy was reported by Xu and coworkers [36]. The reinforcement particles were formed in situ due to intermetallic reactions triggered by the injection of iron-coated boron, pure titanium, and pure aluminum powders in the laser melt pool. The input parameters in the investigation were a CO2 laser power of 1.7 kW and a scanning velocity of 3 mm/s. Surface oxidation was prevented using a coaxial jet and side jet of argon. A distinct relationship of wear resistance with the applied load was observed by the authors (Figure 10.6). When the applied load was low (8.9 N), the wear resistance and hardness of the composite surfaces of the alloy increased with an increase in the volume percentage of titanium diboride (TiB2), iron aluminide (Al3Fe), and titanium aluminide (Al3Ti) dispersions (Samples A to E in figure). This can be explained from the fact that the dispersed particles acted as higher load-bearing phases, preventing the base Al-matrix from getting loaded by the wear balls. However, as the loads were increased (17.8 N, 26.7 N, and 36.9 N), the wear behavior changed and aggravated wear was observed with a higher volume fraction of the dispersion phase. It was concluded that an increase in load increased particle–matrix strain, thereby causing pulling out of reinforced particles. The wear debris of pulled out hard particles initiates third-body abrasive wear on the material surface, significantly deteriorating the wear resistance of the material. Hence, careful material selection and processing techniques should be used, as the wear resistance depends not only on particle distribution and volume percentage but also on the applied load.
Composite Processing Techniques
Published in Andy Nieto, Arvind Agarwal, Debrupa Lahiri, Ankita Bisht, Srinivasa Rao Bakshi, Carbon Nanotubes, 2021
Andy Nieto, Arvind Agarwal, Debrupa Lahiri, Ankita Bisht, Srinivasa Rao Bakshi
Al-CNT composites have been prepared by hot pressing powder mixtures at 520 °C and 25 MPa [14] for more than 30 min. CNT agglomerates were found mainly at the Al grain boundaries, while few single CNTs were found embedded within the matrix. Reaction between Al and CNT leading to compounds with Al:C ratio of 1:1 and 1:2 was observed through EDS. Al-SWNT composites have been prepared by hot pressing of a mixture of nano-Al particles (50 nm in size) and SWNTs at a pressure of 1000 MPa and temperatures between 260 and 480 °C [15]. Ultrasonication was used to disperse the two powders in alcohol, but the composite was found to have CNT agglomerates. No chemical reaction was reported between SWNT and Al. Cu-CNT composites have been prepared by hot pressing ball milled powder mixtures at temperatures of 1100 °C in argon atmosphere in a graphite die at a pressure of 32 MPa [16] for 1 h. Composite with Ni-coated CNT shows better densification and good dispersion of second phase in the matrix, whereas uncoated CNTs segregate at the grain boundaries due to surface tension and poor bonding with the matrix [16]. Mg-CNT composite was prepared by a two-step process of hot pressing in a vacuum at 600 °C at a pressure of 50 MPa for 0.5 h followed by hot isostatic pressing at 600 °C at 180 MPa for 1 h [17]. Ti-20 vol.% CNT composites have been prepared by vacuum hot pressing at 935 °C at a pressure of 30 MPa for 2 h [13]. Figure 3.2b shows the microstructure of Ti-CNT composite showing the presence of CNT clusters. Even though the temperature was high, TiC formation was not observed at the Ti-CNT interface. This study exemplifies the thermal stability of CNTs at high temperature. Vacuum hot pressing has also been used for producing composites of CNTs with novel matrices like iron aluminide (at 1150 °C with 35 MPa for 1 h) [18] and Ti-based bulk metallic glasses (at 450 °C with 1.2 GPa) [19]. Uniform distribution of CNTs throughout the iron aluminide powders has been observed, resulting in improved mechanical properties (hardness, compressive strength, and bend strength). The enhanced mechanical property was also attributed to grain growth inhibition caused by interlocking nanotubes.
On the mechanical response and intermetallic compound formation in Al/Fe interface: molecular dynamics analyses
Published in Philosophical Magazine, 2020
Zeina El Chlouk, Wassim Kassem, Mutasem Shehadeh, Ramsey F. Hamade
A considerable body of work exists in the literature on Al (FCC) / Fe (BCC) systems. Employing EAM, Chung and Chung [4] simulated the growth of Al (FCC) thin film on Fe (BCC) substrate and vice versa. Utilising RDF, depositing Fe on Al substrate was found to result in the creation of FeAl intermetallic compounds including at room temperature and at low kinetic energy values, whereas depositing Al on a Fe substrate shows no intermixing under these conditions. Also, it was found that kinetic energy did not have an effect on the intermixing of the two compounds and the evolution FeAl intermetallic while temperature did. With the aid of 57Fe Mossbauer spectroscopy with respect to crystal orientation, Sule et al. [5] reported similar asymmetry findings to those reported in [4] regarding the growth of Al/Fe interface during mixing between Al and Fe. Employing physical vapour deposition at room temperature, Fonda and Traverse [6] presented evidence of intermixing between iron and aluminium and, consequently, the formation of iron aluminide intermetallic compound at Al/Fe interface. To validate the potential employed in the Modified Embedded Atom Method (MEAM), Hao and Lau [7] employed the second nearest neighbour to examine the interaction of deposited iron on aluminium atoms.
Aluminising of steel with a cathodic arc plasma based method
Published in Transactions of the IMF, 2019
T. Çelikel, E. Kacar, M. Ürgen
Iron aluminide coatings are produced by diffusion processes between the iron-based substrates and Al that is deposited on them. They are generally used for improving high-temperature oxidation and corrosion resistance of steel components.1–3 Aluminide coatings form stable and protective oxides, and they have excellent resistance to gaseous environments containing sulphur compounds.4,5 Therefore, aluminised steel finds applications in coal gasification plants, petroleum refineries, petrochemical industry and coal using energy centres.6,7 Depending on the method of aluminising and process temperature, it is possible to produce coatings that are rich in aluminium or rich in iron. Iron-rich aluminide coatings are of interest due to their higher melting temperatures, toughness, mechanical properties and also the possibility of producing them in ordered structures.8