Page 304 - 00. Complete Version - Progress Report IPEN 2014-2016

304 Materials and Nanotechnology | Progress Report

sonable cost, but also high fatigue resistance. ed by residual stress measurements. The alu-
Moreover, the Al alloy parts have a rather high minum alloys studied are from the Al-Mg-Si
residual value, because the aluminum is fully and Al-Zn-Mg types (6005A, 6082 and 7108).
recyclable at the end of the useful life of the
part. Automotive cylinder liners are mechan- Ti-6Al-4V and γ-TiAl alloys
ical components with the function of being
an internal coating of automotive engine cyl- Ti-6Al-4V alloy has found applications at el-
inders. Among the different foundry casting evated temperatures and as biomaterial. The
methods, the centrifugal casting technique alloy Ti-6Al-4V is one of the most widely used
relies on a tubular die with a high rotation- titanium alloy because of an excellent combi-
al speed during pouring (1,700 rpm). The dy- nation of properties like strength, toughness,
namic effect of the high rotational speed pro- corrosion resistance and chemical stability.
motes high centrifugal acceleration, reduces Surface modification of the Ti-6Al-4V alloy
porosity and promotes some density segre- has been carried out to improve mechanical
gation effect that cannot be achieved in stat- properties at elevated temperatures and fa-
ic foundry processes. The centrifugal casting tigue resistance. The surface modification that
process using the Al-Si alloys for cylinder lin- was carried out was plasma nitriding. The ni-
ers can induce some reduction in the silicon triding was performed by varying parame-
content, mainly with low hypereutectic com- ters as time, temperature and gas mixture in
positions compared to the materials used in the atmosphere. The gas mixture of Ar: N2:
static processes. The high centrifugal acceler- H2 (0.49: 0.49: 0.03) at 700°C for 4 hours was
ation prompts silicon to run mainly in the in- the chosen condiction. Creep and hot tensile
ner diameter direction, due to its lower den- tests were performed to evaluate the mechan-
sity compared to that of the aluminum alloy, ical properties at elevated temperatures and
even in the liquid state. Thus, with low silicon fatigue test at room temperature. The phases
content on the outer side, it becomes easier to of the nitrided sample detected by XRD were
guarantee wear resistance in the cylinder/pis- the ο-Ti2N and ο-TiN, in addition to the ο-Ti
ton and ring working surfaces, as well as the and ο-Ti matrix phases. The layer thickness of
mechanical properties requirements. The alu- this sample was about 1 μm. Hot tensile tests
minum alloys studied are Al-19%Si with addi- were performed in a temperature range from
tions of up to 5%Mg and 5%Cu. 500°C to 700°C in nitrided and no nitrided ma-
terial and show an increase in the strength of
Extruded aluminum alloys find applications the nitrided alloy. The creep tests were also
as automotive components. For automotive performed in a temperature between 500 and
components, adequate mechanical strength/ 700ºC and stress range from 125 to 319 MPa.
weight ratio at a reasonable cost is essential. The result was an increase in creep resistance
Moreover, these materials should be resistant of the nitrided sample. This was evidenced by
to fatigue when used as components exposed both the decrease in secondary creep rate and
to cyclic loads. Precipitation hardening is an im- an increase in final creep time. Fracture of the
portant method used to increase the strength tensile tested specimens was predominant-
of some aluminum alloys. Shot peening is a ly ductile with microcavities. The selected al-
process to cold work the surface and is used to loy after ion implantation by plasma immer-
increase the fatigue life. This can be evaluat- sion was submitted to creep tests at 600°C, in

Instituto de Pesquisas Energéticas e Nucleares