Physical-Mechanical Characteristics and Microstructure of Ti6Al7Nb Lattice Structures Manufactured by Selective Laser Melting

Selective laser melting of titanium matrix composites: An in-depth analysis of materials, microstructures, defects, and mechanical properties

This paper provides an in-depth review of the advancements and challenges associated with Titanium Matrix Composites (TMCs) in Selective Laser Melting (SLM). Material selection, SLM processing parameters, and their influence on the microstructure and properties of TMCs are discussed. The relationship between processing parameters, material characteristics, and the development of defects such as balling, porosity, and cracking is examined. Critical factors influencing the evolution of microstructure and defect formation in TMCs processed by SLM are highlighted. Strengthening mechanisms such as dislocation movements, grain refinement, the Orowan process, and load-bearing capacity are analyzed, and their roles in enhancing hardness, tensile strength, corrosion resistance, and wear resistance are explored. It is indicated by key findings that less than 5 % reinforcement content by volume can significantly enhance mechanical properties, achieving maximum hardness values of approximately 1000 HV and tensile strength close to 1500 MPa. However, this improvement is accompanied by a notable decrease in elongation. The importance of optimizing SLM parameters such as laser power, scan speed, hatch distance, layer thickness, and particle contents to minimize defects and enhance material performance is underscored. Existing research gaps in defect management and material distribution are identified. Future research directions on improving TMCs performance through advanced SLM techniques are suggested.

Effect of Crosshead Speed and Volume Ratio on Compressive Mechanical Properties of Mono- and Double-Gyroid Structures Made of Inconel 718

The current development of additive technologies brings not only new possibilities but also new challenges. One of them is the use of regular cellular materials in various components and constructions so that they fully utilize the potential of porous structures and their advantages related to weight reduction and material-saving while maintaining the required safety and operational reliability of devices containing such components. It is therefore very important to know the properties of such materials and their behavior under different types of loads. The article deals with the investigation of the mechanical properties of porous structures made by the Direct Metal Laser Sintering (DMLS) of Inconel 718. Two types of basic cell topology, mono-structure Gyroid (G) and double-structure Gyroid + Gyroid (GG), with material volume ratios of 10, 15 and 20 %, were studied within our research to compare their properties under quasi-static compressive loading. The testing procedure was performed at ambient temperature with a servo-hydraulic testing machine at three different crosshead testing speeds. The recorded data were processed, while the stress-strain curves were plotted, and Young's modulus, the yield strength Re_0.2, and the stress at the first peak of the local maximum σ_LocMax were identified. The results showed the best behavior under compression load among the studied structures displayed by mono-structure Gyroid at 10 %. At the same time, it can be concluded that the wall thickness of the structure plays an important role in the compressive properties but on the other hand, crosshead speed doesn´t influence results significantly.

Properties Evaluations of Topology Optimized Functionally Graded Lattice Structures Fabricated by Selective Laser Melting

Owning to their lightweight characteristic and high performance, functionally graded lattice structures (FGLSs) show great potential in orthopedics, automotive industries and aerospace applications. Here, two types of uniform lattice structures (ULSs) with RD = 0.50 and 0.20, and two types of FGLSs with RD = 0.30-0.50 and RD = 0.20-0.40, were designed by topology optimization and fabricated by SLM technology. Subsequently, their surface morphology, compressive deformation behavior and energy absorption abilities were evaluated by use of the finite element method (FEM) and compression tests. From these results, both elastic modulus and yield strength of specimens decreased with the lowering of the RD value. ULSs had a uniform deformation behavior with bending and bulking of struts, while FGLSs presented a mixed deformation behavior of different layers. Additionally, the energy absorption capability (W_v) of specimens was proportional to the RD value. When the value of RD increased from 0.20 to 0.50, the W_v of specimens increased from 0.3657 to 1.7469 MJ/m³. Furthermore, mathematical models were established successfully to predict the mechanical properties of FGLSs with percentage deviations < 10%. This work provides a comprehensive understanding regarding how to design and manufacture FGLSs with the properties desired for satisfying the demand of different application scenarios.

Synthesis, Surface Nitriding and Characterization of Ti-Nb Modified 316L Stainless Steel Alloy Using Powder Metallurgy

The powder metallurgy (PM) technique has been widely used for producing different alloy compositions by the addition of suitable reinforcements. PM is also capable of producing desireable mechanical and physical properties of the material by varying process parameters. This research investigates the addition of titanium and niobium in a 316L stainless steel matrix for potential use in the biomedical field. The increase of sintering dwell time resulted in simultaneous sintering and surface nitriding of compositions, using nitrogen as the sintering atmosphere. The developed alloy compositions were characterized using OM, FESEM, XRD and XPS techniques for quantification of the surface nitride layer and the nitrogen absorbed during sintering. The corrosion resistance and cytotoxicity assessments of the developed compositions were carried out in artificial saliva solution and human oral fibroblast cell culture, respectively. The results indicated that the nitride layer produced during sintering increased the corrosion resistance of the alloy and the developed compositions are non-cytotoxic. This newly developed alloy composition and processing technique is expected to provide a low-cost solution to implant manufacturing.