Page 24 - PR 2014 2016 10 Materials and Nanotechnology
P. 24
300 Materials and Nanotechnology | Progress Report
Mechanical and metallurgical properties
of sintered steels for valve seat inserts
application
The aim of this work was to study the valve
seat insert (VSI) obtained with three different
alloys (mainly modified from the original AISI
M3/2, M2 and D2 high-speed steels) from the
mechanical and metallurgical point of view.
These alloys modifications were intended
as an alternative to replace cobalt and lead
used in the original alloy due to their high Figure 32: Micrograph obtained by optical microscopy of Alloy 1
(AISI D2 mixture) air quenched and double tempered at 500 °C.
cost and toxicological effect, respectively.
Such alloys have been developed for inter-
nal combustion engines VSI manufacture. Selective laser melting and precision
The VSI studied in this work was previously casting of the Cobalt-Chromium-
produced by powder metallurgy (P/M) route. Molybdenum alloy
The VSI production was performed by using a
uniaxial hydraulic press and a belt conveyor The mechanical properties and microstructur-
furnace. The VSI was submitted to metallic al characterization of specimens of the Co-Cr-
infiltration during the sintering process us- Mo alloy obtained by additive manufacturing
ing copper as filler (Figure 31). The studies - selective laser melting (SLM) and precision
were performed according to standardized casting (PC) (Figure 33 a and b)- aiming at
apparent density (ASTM C 373-88), apparent the manufacture of dental prosthesis were
hardness (ASTM E 92-82) and radial crush evaluated. The following steps were carried
strength (MPIF Standard 35) tests. The VSI out on Co-Cr-Mo gas-atomized powders: 1)
produced with M3/2 alloy proved to be more investigation of the physical, chemical and
advantageous considering the highest values thermal properties of atomized powders in
obtained in the apparent hardness and radi- different grain sizes (denominated: D1 <15
al crush strength tests. The microstructure μm, D2 20-50 μm and D3 > 75 μm); 2) the
example was presented in figure 32. consolidation of standard specimens via
consolidation techniques; 3) characterization
of consolidated by analysis of: cytotoxicity,
porosity, X ray diffraction and dilatometry;
4) mechanical characterization of tensile, 3
point bending, hardness (macro and micro
Vickers) tests and microstructural character-
ization (OM and SEM-EDS). In general, the
results observed were: the grain size D2 (20-50
μm) is the one that best fits in the analysis of
packaging, for the consolidation by SLM; the
biocompatibility of the samples obtained a
positive result for both processing techniques;
Figure 31: Copper rings (left) and inserts (right) before sintering
process, respectively. the mechanical evaluation of the specimens
Instituto de Pesquisas Energéticas e Nucleares
