| dc.description.abstract | This study aims to enhance the mechanical properties and corrosion resistance of martensitic stainless steel AISI 420 matrix by incorporating Titanium Nitride (TiN) ceramic particles using the selective laser melting (SLM) technique. Furthermore, this investigation provides valuable insights into simultaneously optimizing processing parameters and revealing the crystallography analysis for superior metal matrix composites in detail.
To accomplish the above goals, the primary aim is to achieve a uniform blend of TiN and AISI 420 powder, mitigating the tendency of TiN particles to cluster together. Therefore, identifying an appropriate mixing method is crucial to alleviate agglomeration and contamination, ensuring a consistent mixture suitable for the SLM process. Subsequently, high-quality SLM samples are attained through pre-printing single-track tests to determine the optimal linear energy density range, followed by the printing of three-dimensional samples to assess the effects of various processing parameters, TiN content (0 – 5 in weight percent (wt. %)), TiN particle size (20 µm, 2 µm, and 20 nm), and post-heat treatment on the final quality, encompassing physical, mechanical, and chemical properties. The intricate relationship between Material–Processing–Microstructure–XRD, SEM, EDS, TEM, EBSD, XPS thoroughly examine property.
Moreover, the study proposes a statistical methodology to optimize the mechanical properties of SLM TiN/AISI 420 samples, employing an integrated approach incorporating Taguchi – Grey Relational Grade – Principle Component Analysis (Taguchi-GRA-PCA). This facilitates decision-making across multiple response variables, particularly on parameters closely associated with mechanical properties such as surface roughness, relative density, and hardness. A key objective is to forecast the optimal strength properties of the SLM sample.
Consequently, we proposed a novel two-stage hybrid mixing method using the blending and vibration in hexane or ethanol solvent. This method ensures the creation of a contaminant-free mixture with homogeneous dispersion of TiN, avoiding agglomeration, to serve as the ideal feedstock for the SLM process. In addition, the Linear Energy Density (LED) was determined in a range of 0.45 to 1.25 J/mm to achieve stable single tracks. The Volume Energy Density (VED) in the 151 to 525 J/mm3 range fabricated a high density of samples.
Various TiN content added into the AISI 420 matrix indicated the different effects on the microstructure, mechanical, and corrosion properties of the SLM TiN/AISI 420 parts. TiN content below 1 wt.% exhibited improvements in mechanical and corrosion resistance ability. Conversely, surpassing 1 wt. % of TiN led to a decline in mechanical properties compared to the base material. Nonetheless, the presence of TiN within the AISI 420 matrix significantly enhanced corrosion resistance.
The heat treatment process decreased the hardness of all SLM TiN/AISI 420 samples, although the tensile properties and corrosion ability increased compared to the as-built state. Using Taguchi-GRA-PCA analysis, optimal processing parameters for achieving the best mechanical properties were determined: laser power of 350W, a laser scanning speed of 370 mm/s, hatch distance of 0.07 mm, and layer thickness of 0.05 mm for 1 wt. % TiN/AISI 420 composites powders.
Following microstructure analysis, the optimal TiN particle content demonstrated even dispersion within the grain boundaries of AISI 420 during the SLM. Including TiN particles in the AISI 420 matrix offered several advantages, as a reinforced phase to fortify the matrix and forming a second passive film of TiN with the initial Cr2O3 film to augment corrosion resistance. The findings revealed SLM TiN/AISI 420 samples, with 1 wt.% TiN reinforcement, achieved a peak hardness of 745 ± 20 HV at a VED of 250 J/mm3, surpassing established benchmarks. Tensile strength reached 1822 ± 21 MPa, with an elongation of 6.41 ± 0.40% and a maximum modulus of toughness at 99.7 ± 3.0 J/m3. Upon subjecting the SLM TiN/AISI 420 samples to post-heat treatment, the toughness increased to 118.0 ± 1.3 J/m3. The optimal SLM TiN/AISI 420 samples exhibited corrosion rate values of 92.8 ± 1.1 mm/year in FeCl3 and 0.78 ± 0.01µm/year in NaCl 3.5%, outperforming those of SLM raw AISI 420.
Overall, this study presents a comprehensive approach to the effect of laser energy, content, and size of reinforced TiN powders and the post-heat treatment on the properties of SLM TiN/AISI 420 samples. It also proposes initial optimization processing parameters to enhance the mechanical properties and corrosion resistance of SLM TiN/AISI 420. The findings of this study offer valuable insights for developing advanced metal matrix composites for various industry applications. | en_US |