Thermodynamic Behavior of Fe-Mn and Fe-Mn-Ag Powder Mixtures during Selective Laser Melting

Abstract

Additive manufacturing is a form of powder metallurgy, which means the properties of the initial metal powders (chemical composition, powder morphology and size) impact the final properties of the resulting parts. A complete characterization, including thermodynamic effects and the behavior of the metal powders at elevated temperatures, is crucial when planning the manufacturing process. The analysis of the Fe-Mn and Fe-Mn-Ag powder mixtures, made from pure elemental powders, shows a high susceptibility to sintering in the temperature interval from 700 to 1000 °C. Here, numerous changes to the manganese oxides and the αMn to βMn transformation occurred. The problems of mechanically mixed powders, when using selective laser melting, were highlighted by the low flowability, which led to a less controllable process, an uncontrolled arrangement of the powder and a large percentage of burnt manganese. All this was determined from the altered chemical compositions of the produced parts. The impact of the increased manganese content on the decreased probability of the transformation from γ-austenite to ε-martensite was confirmed. The ε-martensite in the microstructure increased the hardness of the material, but at the same time, its magnetic properties reduce the usefulness for medical applications. However, the produced parts had comparable elongations to human bone.

Additive Manufacturing of Fe-Mn-Si-Based Shape Memory Alloys: State of the Art, Challenges and Opportunities

“…Regarding the composition, the presence of Mn oxides is also usual. Kraner et al [112] reported that manganese is liable to oxidate during the atomization of the powders, so the oxygen is carried into the matrix, along with the Mn, forming Manganese oxides that do not dissolve into the matrix. In our case, the Aluminum, which comes from the impurities of the master alloys, just happens to replace de role of the Mn (Mn 2 O 3 ), leading to those mixed oxides of (Al,Mn) 2 O 3 type.…”

Adjustment of AgCaLa Phases in a FeMn Matrix via LBM for Implants with Adapted Degradation

“…The incorporation of the slag into AgCaLa is conclusive due to the lower surface tension and melting temperature of AgCaLa. Since the oxides of Mn decompose and melt at high temperatures, incorporation to FeMn with high melting temperature is less probable [46,110,111]. Additionally, the slag is located on the top of AgCaLa, and AgCaLa lies on FeMn; thus, the slag is in contact with AgCaLa and not with FeMn.…”

“…Powder-based metallurgical processes such as laser beam melting enable the processing of such materials, as mechanically mixed powders can be used [29,44,45]. Due to the small melt pool, strong melt flow, as well as rapid melting and solidification, homogenous and adaptable Ag phases in an iron-based matrix can be obtained via LBM [26,35,46,47]. Apart from the morphology of the Ag phases, the chemical composition has to be addressed.…”

Modification of Iron with Degradable Silver Phases Processed via Laser Beam Melting for Implants with Adapted Degradation Rate

“…[ 60–64 ] Laser beam melting (LBM) is characterized by small melt pools with strong melt flow as well as rapid melting and solidification which enables the processing of such materials. [ 27,65–68 ] Following crucial aspects of the LBM process, on which the conducted research is based, are presented. The short exposure time to high temperatures during LBM is beneficial for the processing of degradable Ag alloys as the time for diffusion of alloying elements between both components is limited.…”