Page 19 - PR 2014 2016 10 Materials and Nanotechnology
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Materials and Nanotechnology | Progress Report 295
Mechanical Properties at 300°C for 5 h. Preliminary results show the
occurrence of DSA in the (b) and (c) conditions.
Fracture mechanics and mechanical
properties of metals, alloys and A fracture mechanics analysis of flaws in grind-
composites ing balls mills for mining plants was undertak-
en and the theoretical values of growth rate
An elastic-plastic fracture mechanics study of those defects were compared with actual
of the application of Leak-Before-Break (LBB) values obtained through periodic inspections
concept in a relatively small-diameter (273 performed in this component. The cracks nu-
mm diameter) high-energy nuclear reactor cleation was caused by lack of lubrication in
coolant line was done, where it is proposed the trunnion bearings, generating circumfer-
AISI 316LN type stainless steel to be used as ential thermal stresses and the estimated tem-
base material welded with AISI 316L coat- perature of the trunnion and bushing contact
ed electrode. Results show a well-defined reached 150°C. During the analyzed period,
mechanical behavior where base material the results obtained by the BS7910 standard
has a high toughness, weld region has a low proved to be closer to the actual values than
toughness, and HAZ shows intermediate the ASME Section XI standard.
properties. For the load limit analysis, the
lowest critical crack size was found for base A study of the influence of solution heat treat-
material presenting circumferential cracks. ment temperature on the hardness response in
For J-integral analysis, it was demonstrated incoloy 945 was done. Incoloy 945 is a hybrid
that tearing instability leading to failure Ni-Fe-Cr based superalloy with a mechanical
would not occur. strength and corrosion resistance comparable
to those of Inconel 718 and Incoloy 925, respec-
A preliminary draft version of a surveillance tively, with minimum yield strength reaching
program for the materials presented in the 860 MPa. The heat treatment at 1000°C causes
nucleus of Brazilian Multipurpose Reactor a hardness reduction around 61%, reaching
(RMB) was developed. The surveillance pro- 63% at the temperature of 1020°C. The reasons
gram is needed to confirm and determine for the reductions are the dissolution of the
the effects of radiation on the mechanical gamma prime hardening phase and a slight
properties of the core reactor materials: its grain growth (ASTM 7). Above this temperature,
effects on the tensile properties (strength and the hardness loss is negligible, however, grain
ductility), fracture toughness, radiation-in- growth is more pronounced reaching a ASTM
duced growth and corrosion. 2 grain size in the specimens treated at 1050°C.
The mechanical behavior of high strength Aluminum alloys for automotive
aluminum alloys of the 7075 series is under applications
investigation, to study the occurrence of dy-
namic strain aging (DSA: Portevin-Le Chat- Automobile parts made of steel/cast iron have
ellier effect) on tensile specimens, submitted been replaced with those made with alumi-
to different heat-treatment conditions: (a) num alloys to not only reduce weight, but also
solution heat treated then artificially aged, to reduce fuel consumption the emission of
T6, (b) T6 then solution heat treated at 485°C pollutants. Structural materials require not
for 5 hours, (c) T6 then solution heat treated only high strength/weight ratio, besides rea-
