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Comportamento a creep e fenomeni di precipitazione nella lega Ni-22Cr-12Co-9Mo A 700 e 800°C
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Creep behaviour of INCOLOY alloy 617
No full textThe microstructural features of INCOLOY
alloy 617 in the solution annealed condition and after longterm
creep tests at 700 and 800 C were characterized and
correlated with hardness and creep strength. Major precipitates
included (Cr,Mo,Fe)23C6 carbides and the
d-Ni3Mo phase. M6C and MC carbides were also detected
within the austenitic grains. However, minor precipitates
particularly c¢-Ni3(Al,Ti) was found to play an important
role. At different exposure temperatures, the microstructural
features of the Ni–22Cr–12Co–9Mo alloy changed
compared with the as-received condition. The presence of
discontinuously precipitated (Cr,Mo,Fe)23C6 carbides and
their coarsening until the formation of an intergranular film
morphology could be responsible both for a reduction in
rupture strength and for enhanced intergranular embrittlement.
The fraction and morphology of the c¢-phase, precipitated
during exposure to high temperature, also
changed after 700 or 800 C exposure. At the latter test
temperature, a lower volume fraction of coarsened and
more cubic c¢ precipitates were observed. These microstructural
modifications, together with the presence of the
d-phase, detected only in specimens exposed to 700 C,
were clearly responsible for the substantially good creep
response observed at 700 C, compared with that found at
800 C
DSC analysis of strengthening precipitates in ultrafine Al-Mg-Si alloys
No full textEqual channel angular pressing (ECAP) was carried out on solution annealed samples of Al–Mg–Si–Zr and Al–Mg–Si–Zr–Sc alloys to achieve a substantial grain refinement of the materials. Post ECAP aging was then investigated on the ultrafine grained alloys by DSC and TEM analyses.
DSC scans were carried out with heating rates ranging from 5 to 30°C min–1. Peak identification was performed by the support
of literature information and TEM analyses. Precipitation kinetics revealed to be similar for both alloys but the Sc-free alloy showed
a recrystallization peak at temperatures ranging from 310 to 340°C, depending on the strain accumulated during ECAP. On the contrary, the Sc-containing alloy showed a greater grain stability. Analyses of peak positions and of activation energies as a function of ECAP passes experienced by the samples revealed large modifications of precipitation kinetics in the ultrafine-grained alloys with respect to the coarse-grained materials
Heat treatment cycle optimization for A707L5 copper-nickel steel
Full text linkThe mechanical properties of the A707L5 steel grade were studied as a function
of the applied aging temperature. The results obtained are discussed on the basis of the
microstructure analysis and precipitates were identified on the fracture surfaces observed
by scanning electron microscopy assisted by a field emission gun (FEG-SEM). This steel grade
appears to be particularly sensitive to the aging time-temperature, which significantly affected
the precipitation phenomena. The annealing temperature and solution quenching
involved in the thermal cycle significantly affect the perlite formation, the grain size and
the ε-Cu precipitates that represent the main factors of influence ruling the mechanical
properties
Thermal analysis of Al-Cu-Mg-Si alloy with Ag/Zr additions
No full textHeat-treatable aluminium alloys are widely used for structural applications. Their strength is obtained through age hardening
phenomena, that are sensitive to microalloying.
In the present paper the results of thermal analyses on the ageing behaviour of an Al–Cu–Mg–Si alloy with silver and
zirconium additions are presented. Specimens were water quenched after solution heat treatment, then aged at 453 K and a
hardness-versus-time plot was drawn. Samples representative of different ageing conditions were subjected to DSC scans.
Peaks were identified taking into account and Q phases precipitation sequences. Solution treated samples showed
GP///Q sequence, while in peak aged condition GP and precipitation peaks disappeared and a reduction of peak area was
observed, witnessing the concurrent presence of and phases at peak hardness condition. Experimental data were compared with
results from analogous investigations performed on a conventional commercial Al–Cu–Mg–Si alloy
Investigation on precipitation phenomena of Ni-22Cr-12Co-9Mo alloy aged and crept at high temperature
Full text linkThe Ni–22Cr–12Co–9Mo alloy (UNS alloy N06617, also known as alloy 617), of relatively common use at high temperature, is also
one of the candidate materials for the most ambitious EU and US projects for future generations of power plants. Its microstructure in
the solution-annealed condition and after long-term creep tests at 700 and 800 1C was characterized by means of light optical, scanning
electron and transmission electron microscopy. Differential scanning calorimetry (DSC) analyses were also performed to check the
usefulness of this technique to detect microstructural modification in specimens exposed to high temperature. Microstructural features
were correlated to the hardness evolution in a chronological range of several thousand hours.
The major microstructural features were identified to be the presence of inter- and/or intragranular particles ((Cr,Mo,Fe)23C6 and
other types of carbides, d-Ni3Mo and g0-Ni3(Al,Ti)) that clearly played an important role in the mechanical behaviour of the alloy. The microstructural features of the investigated alloy changed at different exposure temperatures (and times) with respect to the as-received condition. The observed microstructural instability of the alloy suggested that creep data obtained at the highest temperature should be very carefully considered in extrapolating the creep strength of the alloy at about 700 1C, since they should lead to a substantial underestimation of the creep life
Laser welding of niobium to 410 steel with a nickel interlayer produced by electro spark deposition
No full textSome combination of metals such as niobium to stainless steel cannot be joined directly by laser welding due to formation of deleterious phases. On the other hand placement of a narrow strip of a third alloy between the two metals can introduce many technical and availability limitations. In this work, a more versatile method is developed using electrospark deposition (ESD) for facilitation of subsequent Nb to 410 stainless steel dissimilar laser with minimum heat input successfully. The 1 mm Nb plate edge was clad by Alloy 82 using a 4 mm round electrode by ESD process. The layer has minimum dilution with Nb while having a metallurgical bond. It exhibited a fine cellular structure with Laves phase particles with 30–50 nm in diameter. The Nb plate with edge built up was then laser welded to 410 stainless steel using a 1 KW fiber laser machine. The presence of the interlayer material suppressed the formation of Nbsingle bondFe intermetallic in the laser fusion zone and increases weldability. Tensile test of dissimilar laser weld with the nickel base ESD interlayer exhibited an ultimate strength of 285 MPa with the failure located at the Nb side and not in laser weld metal or at the ESD interface
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