Page 308 - 00. Complete Version - Progress Report IPEN 2014-2016

308 Materials and Nanotechnology | Progress Report

Mechanical and metallurgical
properties of sintered steels for
valve seat inserts application

Figure 31: Copper rings (left) and inserts (right) be-
fore sintering process, respectively.

The aim of this work was to study the valve Figure 32: Micrograph obtained by optical microscopy of Alloy 1
seat insert (VSI) obtained with three different (AISI D2 mixture) air quenched and double tempered at 500 ºC.
alloys (mainly modified from the original AISI
M3/2, M2 and D2 high-speed steels) from the The mechanical properties and microstructural
mechanical and metallurgical point of view. characterization of specimens of the Co-Cr-Mo
These alloys modifications were intended as alloy obtained by additive manufacturing - se-
an alternative to replace cobalt and lead used lective laser melting (SLM) and precision cast-
in the original alloy due to their high cost and ing (PC) (Figure 33 a and b)- aiming at the man-
toxicological effect, respectively. Such alloys ufacture of dental prosthesis were evaluated.
have been developed for internal combustion The following steps were carried out on Co-Cr-
engines VSI manufacture. The VSI studied in Mo gas-atomized powders: 1) investigation of
this work was previously produced by powder the physical, chemical and thermal properties
metallurgy (P/M) route. The VSI production of atomized powders in different grain sizes
was performed by using a uniaxial hydraulic (denominated: D1 <15 μm, D2 20-50 μm and
press and a belt conveyor furnace. The VSI was D3 > 75 μm); 2) the consolidation of standard
submitted to metallic infiltration during the specimens via consolidation techniques; 3)
sintering process using copper as filler (Figure characterization of consolidated by analysis
31). The studies were performed according to of: cytotoxicity, porosity, X ray diffraction and
standardized apparent density (ASTM C 373- dilatometry; 4) mechanical characterization
88), apparent hardness (ASTM E 92-82) and ra- of tensile, 3 point bending, hardness (macro
dial crush strength (MPIF Standard 35) tests. and micro Vickers) tests and microstructural
The VSI produced with M3/2 alloy proved to characterization (OM and SEM-EDS). In gen-
be more advantageous considering the high- eral, the results observed were: the grain size
est values obtained in the apparent hardness D2 (20-50 μm) is the one that best fits in the
and radial crush strength tests. The micro- analysis of packaging, for the consolidation
structure example was presented in figure 32. by SLM; the biocompatibility of the samples
obtained a positive result for both processing
Selective laser melting and techniques; the mechanical evaluation of the
precision casting of the Cobalt- specimens shows that the SLM technique pro-
Chromium-Molybdenum alloy vides superior mechanical properties (yield

Instituto de Pesquisas Energéticas e Nucleares