Materials Science Forum Vol. 1146

Abstract: A new technology of titanium metal powder production by means of two stages reduction of titanium dioxide, using magnesium and calcium, has been developed and patented by VELTA, Ukraine. In addition to the grades of pure metal titanium, the proposed technological scheme makes it possible to obtain various titanium alloys powders by joint reduction of titanium dioxide with oxides of alloying elements. The powder consists of compact particles with a low content of interstitial elements oxygen, nitrogen and carbon under the levels of standard for Ti Grade 1. A particle size measurement shows a broad distribution with D50 near 50 µm with a large number of very fine, almost spherical particles under 2 µm. A classification of the produced powder by a relatively cheap sieving technology into fractions makes it suitable for different powder metallurgical applications, particularly in Metal Injection Moulding (MIM) technology. The fraction of the powder under 45 µm (35 wt.% of the product) has been tested for MIM technology. Two types of feedstock (catalytic and water-soluble) were used in the study. Sintered samples comply with Ti-400 standard for MIM components used in medical, chemical, aerospace and other industries.

Abstract: For the processing of metal powders by Metal Injection Moulding (MIM) or indirect methods of Additive Manufacturing (AM), such as material extrusion (MEX-AM) polymers of different kinds are employed. Usually, the task of these polymers is to enable the shaping of a certain geometry and to maintain this shape down to the first cohesive effects of sintering. Nowadays, for the production of metal parts one goal is to get rid of the polymer as complete as possible. Another possibility is to use the polymer or at least part of it, mainly the carbon, for the metallurgical process of forming the final part in sintering as a process of heat treatment. Titanium is a metal, which is reacting with carbon easily. The question in focus here is how to utilise the carbon or some of it in the powder metallurgical processing of titanium. For first steps into this question, we selected two different powders, CPTi and TiH₂, and mixed them with two different polymers, polypropylene PP and low-density polyethylene LDPE. As a compatibilizer stearic acid SA was used. The polymers were selected because they are normally used as backbone in binder systems, and show a significantly different thermal degradation behaviour. Thus, the amount and type of carbon during thermal degradation could be expected to be different. The study comprises the preparation of polymer-powder blendings with up to 80 vol.% powder to resemble the conditions after solvent debinding; the shaping in discs, and TG-DTA experiments in air and in Ar to find out the temperature of backbone removal (Tr). Isothermal experiments are also done to know about the polymer removal with time. The different interaction of the polymers with the titanium powders is investigated, with a special attention to the interaction of hydride decomposition and polymer degradation. Keywords: Metal Injection Moulding; indirect Additive Manufacturing; titanium and titanium alloys; powder-polymer interaction

Abstract: The characteristics of β-phase metastable Ti alloys make them an attractive choice for advanced engineering applications in demanding conditions. Ti-35Nb alloy has high strength-to-weight ratios, deep hardenability and high biocompatibility exhibiting high potential for use in niche applications for aircraft structures, orthopedic implants, and orthodontic devices. The difficulty of producing complex shapes of these alloys by conventional methods for reasonable costs makes Metal Injection Moulding (MIM) attractive. Sintering behavior, microstructure and mechanical properties of a Ti–35Nb alloy processed by MIM technology from hydrided powders were investigated in this work by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermal and microhardness analysis. Samples with relative density up to 93% have been produced using a feedstock based on wax-polymer binder. The microstructural evolution observed during sintering from 900 °C up to 1500 °C indicates a combination of densification and optimized microstructure reached because of the complete dissolution of the β stabilizer (Nb) in the titanium matrix. The injection and sintering parameters provided a homogeneous microstructure with some TiC precipitates at grain boundaries and relative high porosity. Higher sintering temperatures or longer holding times can lead to intensive grain growth.

Abstract: This study delves into the nuanced challenges of additive manufacturing, specifically focusing on the application of sinter-based processes for reactive materials, with Titanium as the focal point. The thermal debinding and sintering processes, crucial steps in shaping, are analyzed with an emphasis on the intricate control required for the removal of polymeric binders, especially concerning the reactivity of metals during these processes. Historically, the emphasis has been on materials like 316L and 17-4-PH due to their straightforward thermal debinding and sintering processes. However, the shift to Titanium and its alloys introduces complexities, requiring special debinding and meticulous control of interstitial elements such as C and O to adhere to stringent material standards such as ASTM F2885-17. This research examines the various stages of shaping progressions, addressing specific requirements like green part strength, flexibility (filaments), flowability (Metal Injection Molding), and crosslinking (Stereolithography). The focus lies on achieving thermal removal with minimal residuals and reactivity, particularly in the context of reactive metals. Lithography-Based Metal Manufacturing (LMM) and Cold Metal Fusion (CMF) emerge as significant additive manufacturing processes for small to medium-sized batches of titanium parts, utilizing sinter-based production setups. Both processes not only serve as alternatives to Metal Injection Molding but also contribute to cost-effectiveness and sustainability through the efficient reuse of unused feedstock. The selection of the optimal shaping technology for individual parts becomes critical, considering mechanical properties, final density, acceptance of interstitials, complexity, wall thickness, overhangs, and internal structures. This presentation provides a detailed analysis of Lithography-Based Metal Manufacturing, comparing it with the Cold Metal Fusion process. Key considerations include mechanical properties, surface finishes, and cost, shedding light on the technical intricacies and trade-offs inherent in each technology.