Application of Direct Current Plasma Sintering Process in Powder Metallurgy

Direct current (dc) plasma-assisted sintering of metal parts is a promising and relatively new research and development field in powder metallurgy (PM). In the present entry, it is intended to introduce the reader to the main applications of the dc plasma sintering process in PM. To achieve this goal, the present entry is divided in a brief introduction and sections in which the bases of the dc plasma abnormal glow discharge regime and its influence in the sintering process are carefully treated. In this case, a clear language is purposely used to didactically introduce the reader to this “fascinating glow world”, the dc plasma-assisted sintering of metal parts, aiming to put in evidence the main points on physicochemical aspects of the plasma environment, basic knowledge of the plasma heating, and surface-related phenomena during dc plasma sintering of parts. All these aspects are treated considering the main techniques of the dc plasma-assisted sintering process applied to PM. Finally, some results on DC plasma heating, sintering and surface modification are presented

Produção e caracterização de uma liga Fe-Ni obtida por processamento coloidal aquoso e reação de estado sólido

O processamento coloidal é uma técnica amplamente usada para a produção de componentes cerâmicos. Diversos artigos científicos foram publicados na última década apresentando a possibilidade de se obter suspensões aquosas concentradas estáveis de partículas metálicas a partir do seu controle de pH e uso de dispersantes. Este artigo tem o objetivo de estudar a produção de um aço com microestrutura austenítica usando pós elementares de ferro (Fe) e níquel (Ni) via rota coloidal. Para tanto, foram realizadas medições de potencial zeta entre os pHs 2 e 12 para a composição Fe30Ni em massa. As suspensões aquosas atingiram concentrações de sólidos de até 45% v/v e processadas por colagem de barbotina. Os compactados colados foram caracterizados por densidade (Arquimedes), análise térmica diferencial (ATD) e dilatometria. Após a sinterização aos 900°C e 1100°C/1h, os compactados apresentaram microestrutura com formação de maclas de recozimento, porosidade inferior a 10% em volume e microdureza Vickers aproximada de 160 HV.Palavras-chave: Reologia, ligas metálicas e colagem de barbotina

Rheological properties of alumina injection feedstocks

The rheological behavior of alumina molding feedstocks containing polyethylene glycol (PEG), polyvinylbutyral (PVB) and stearic acid (SA) and having different powder loads were analyzed using a capillary rheometer. Some of the feedstocks showed a pseudoplastic behavior of n < 0, which can lead to the appearance of weld lines on molded parts. Their viscosity also displayed a strong dependence on the shear rate. The slip phenomenon, which can cause an unsteady front flow, was also observed. The results indicate that the feedstock containing a lower powder load displayed the best rheological behavior. The 55 vol. % powder loaded feedstock presented the best rheological behavior, thus appearing to be more suitable than the formulation containing a vol. 59% powder load, which attained viscosities exceeding 10³ Pa.s at low shear rates, indicating its unsuitability for injection molding