Tecnologia em Metalurgia, Materiais e Mineração
https://tecnologiammm.com.br/article/doi/10.4322/tmm.2011.024
Tecnologia em Metalurgia, Materiais e Mineração
Artigo Original

NUCLEAÇÃO DE TRINCAS EM MOLDES DE INJEÇÃO DE ALUMÍNIO COM TRATAMENTO DE SUPERFÍCIES DUPLEX

CRACK NUCLEATION IN ALUMINIUM INJECTION DIES WITH DUPLEX SURFACE TREATMENT

Gallo, Santiago Corujeira; Tomiello, Stevan Scussel; Gaboardi, Rodrigo; Figueroa, Carlos Alejandro; Baumvol, Israel Jacob R.

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Resumo

Neste trabalho é estudada a geração prematura de trincas em um molde para injeção de alumínio com tratamento superficial duplex (nitretação a plasma e revestimento por deposição física em fase vapor, PVD). Foram registradas as condições de fabricação e de operação do molde e o estudo da falha incluiu as seguintes técnicas analíticas: medição do perfil de dureza, identificação de fases por difração de raios X e observações metalográficas por microscopia óptica e por microscopia eletrônica de varredura. Esta última técnica possui a capacidade de análise de composição química por dispersão de energia de raios X. As observações preliminares revelam uma microestrutura grosseira da martensita revenida e uma rugosidade superficial considerável. A análise detalhada dos sítios de nucleação das trincas mostra a presença de inclusões de enxofre entre o substrato e o revestimento. A presença do enxofre é atribuída à utilização de pedras enxofradas no polimento final do molde. O mecanismo de falha é apresentado com base nessas evidências.

Palavras-chave

Injeção de alumínio, Fadiga térmica, Nitretação, Revestimento PVD

Abstract

The premature nucleation of cracks in an aluminum injection die with duplex surface treatment (plasma nitriding and physical vapor deposition coating, PVD) is studied. The manufacturing and operating conditions were documented and the study included the following analytical techniques: hardness profile, X-ray diffraction for phase identification, microscopic observations by optical microscopy, scanning electron microscopy The latter with energy dispersive X-ray has the capability for chemical analysis. Preliminary observations reveal a microstructure consisting of coarse tempered martensite and a considerable surface roughness. A detailed analysis of crack initiation sites shows the presence of sulfur inclusions between the substrate material and the coating. The presence of sulfur is attributed to the use of sulfur impregnated grinding stones in the final polishing of the die. Consequently, the failure mechanism is presented in view of this evidence.

Keywords

Aluminum injection, Thermal fatigue, Nitriding, PVD coatings

Referências

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