Influence of particle-size distribution and temperature on the rheological properties of highly concentrated Inconel feedstock alloy 718

• Published in: Powder technology 2017-12, Vol.322, p.273-289
• Main Authors: Dimitri, Claudel, Mohamed, Sahli, Thierry, Barriere, Jean-Claude, Gelin
• Format: Article
• Language: English
• Subjects: Activation energy; Alloy steels; Carbides; Inconel superalloy; Injection; Injection molding; Mathematical models; Mechanics; Modelling; Molding (process); Nickel base alloys; Particle size; Particle size distribution; Physics; Polyethylene; Polyethylene glycol; Polypropylene; Powder; Powder injection moulding feedstock; Pseudoplasticity; Raw materials; Rheological properties; Rheology; Rheology models; Shear rate; Shrinkage; Sintering (powder metallurgy); Size distribution; Solids; Stainless steel; Stearic acid; Superalloys; Temperature
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2017.08.049

Powder injection moulding is a low-cost manufacturing process that produces very complex parts to net shapes in a wide variety of materials and unique alloys, including superalloys, stainless steels, and carbides. The feedstocks used in this process must meet various requirements. They have to show good flowability for the injection process, but they also need to have high solids loading to reduce shrinkage during sintering. In the present study, we investigated the rheological behaviours of Inconel feedstock with various average particle sizes in a polydisperse population from 6 to 66μm and solids loading (ϕ=50%–72%) at a shear rate of 10–105s−1. The binder formulation was a polymer-based aqueous system composed of 55vol% polyethylene glycol (PEG), 40vol% polypropylene (PP), and 5vol% stearic acid (SA). In particular, the effects of particle size, flow activation energy and the mouldability index on the rheology of the feedstock were studied in detail. New rheological models that describe the effects of various parameters such as shear rate, particle size, temperature, and solids loading are introduced, and their predictions are compared with the experimental values. These rheological behaviours were also characterised using our empirical models, which can be directly applied to the process optimisation of powder injection moulding for micro-components. As a result, rheological parameters such as flow behaviour index, maximal solids loading, and flow activation energy were obtained. The particular rheological behaviour of the Inconel feedstock with a highly concentrated solids fraction, which deviates from typical pseudoplastic behaviour, has a relevant correlation with the proposed models. Moreover, the models can be used when similar behaviours are observed in other formulation, powder and binder systems. [Display omitted] •Inconel superalloy powder and polymer based PEG aqueous binder systems are mixed.•Influence of particle size, temperature and solid loading on shear rheology is shown.•New rheological models for high loaded polymer•Identifications of rheological models are carried out for feedstocks and binders.•Influence of the powder particle size on the mouldability index