Comparison of Single Ti6Al4V Struts Made Using Selective Laser Melting and Electron Beam Melting Subject to Part Orientation

Abstract

Abstract:The use of additive manufacturing technologies to produce lightweight or functional structures is widespread. Especially Ti 6 Al 4 V plays an important role in this development field and parts are manufactured and analyzed with the aim to characterize the mechanical properties of open-porous structures and to generate scaffolds with properties specific to their intended application. An SLM and an EBM process were used respectively to fabricate the Ti 6 Al 4 V single struts. For mechanical characterization, uniaxial compression tests and hardness measurements were conducted. Furthermore, the struts were manufactured in different orientations for the determination of the mechanical properties. Roughness measurements and a microscopic characterization of the struts were also carried out. Some parts were characterized following heat treatment (hot isostatic pressing). A functional correlation was found between the compressive strength and the slenderness ratio (λ) as well as the equivalent diameter (d) and the height (L) of EBM and SLM parts. Hardness investigations revealed considerable differences related to the microstructure. An influence of heat treatment as well as of orientation could be determined. In this work, we demonstrate the influence of the fabrication quality of single struts, the roughness and the microstructure on mechanical properties as a function of orientation.

Micro-Macro Relationship between Microstructure, Porosity, Mechanical Properties, and Build Mode Parameters of a Selective-Electron-Beam-Melted Ti-6Al-4V Alloy

“…Nevertheless, the mechanical performances of SEBM-manufactured Ti-6Al-4V and Ti-6Al-4V ELI alloy products [10,12,[14][15][16] compare well with those fabricated by means of SLM [8,[12][13][14] and those produced by means of conventional casting and wrought routes [14,17].…”

“…Such a unique combination is particularly advantageous for lightweight applications or whenever high specific mechanical properties and cost advantages are favorable compared to conventional machining [4,7].SEBM has become a mature technology that can rely on an extensive amount of literature, which aids the development of new applications [6]. Powder flowability plays a crucial role in the initial raking of layers which, in turn, determines the optimal density and homogeneity of a microstructure after solidification [7].Solidified SEBM microstructures are relatively fine [8,9] and frequently free of martensite, unless special SEBM conditions or very fine powders are selected, or very thin parts are fabricated [3,10,11].The absence of martensite is one of the main causes of the observed reduced mechanical properties of SEBM products compared to their selective laser melting (SLM) counterparts [12][13][14], although additional factors, such as the initial powder (average size and size distribution), part thickness, and oxygen uptake, are also relevant.Nevertheless, the mechanical performances of SEBM-manufactured Ti-6Al-4V and Ti-6Al-4V ELI alloy products [10,12,[14][15][16] compare well with those fabricated by means of SLM [8,[12][13][14] and those produced by means of conventional casting and wrought routes [14,17].It has been shown that a large range of other outstanding properties [10,12,15,18,19] can currently be achieved in SEBM-manufactured builds as a result of a better understanding of the interrelationship between process parameters (e.g., scan speed, offset focus and beam current, beam current, layer feed, offset focus, and melting paths, etc.) and of such crucial factors as microstructure [10][11][12][14]…”

“…The absence of martensite is one of the main causes of the observed reduced mechanical properties of SEBM products compared to their selective laser melting (SLM) counterparts [12][13][14], although additional factors, such as the initial powder (average size and size distribution), part thickness, and oxygen uptake, are also relevant.…”

“…It has been shown that a large range of other outstanding properties [10,12,15,18,19] can currently be achieved in SEBM-manufactured builds as a result of a better understanding of the interrelationship between process parameters (e.g., scan speed, offset focus and beam current, beam current, layer feed, offset focus, and melting paths, etc.) and of such crucial factors as microstructure [10][11][12][14][15][16][20][21][22][23][24], chemical composition [14,25], particle size and distribution of pre-alloyed powders [26], the electrostatic charge effect in the powder [22], powder pre-heating [22,23], sintering conditions of the powder (prior to melting) [22,24], build thickness [11,14,15], surface quality (i.e., roughness and topography), [14,15], grindability (to minimize wear resistance and dissipation by friction) [12,21], bioreactivity [21], corrosion resistance [12], porosity [10,11,[14][15][16]23,24,27], building orientation (horizontal and vertical) [10,14], distance from the build plate…”

Advancements in three-dimensional titanium alloy mesh scaffolds fabricated by electron beam melting for biomedical devices: mechanical and biological aspects

“…This suggested that the surface properties can be tailored by adjusting the scan speed of the electron beam. Other researchers observed that the orientation during the building process had an influence on surface roughness because of change in energy flow [78,79].…”