Influence of Thermal and Thermo-Mechanical Processing on the Creep Resistance of Mg-10Gd-3Y-0,4Zr Alloy

2011 ◽  
Vol 675-677 ◽  
pp. 487-490 ◽  
Author(s):  
Vit Janik ◽  
Qu Dong Wang ◽  
Dong Di Yin ◽  
Wen Jiang Ding
Keyword(s):  
Grain Boundaries ◽  
Creep Resistance ◽  
Tensile Creep ◽  
Secondary Phases ◽  
Lower Cavity ◽  
Creep Cavitation ◽  
Peak Aged ◽  
High Fraction ◽  
Aged State ◽  
Minimal Creep Rate

Alloy Mg-10Gd-3Y-0,4Zr in as-cast, as-extruded, cast-T6 (peak aged) and extruded-T5 (peak aged) state was tensile creep tested at 200, 250 and 300 °C and stress 50, 80 and 120 MPa. Comparison of minimal creep rate shows that alloy Mg-10Gd-3Y-0,4Zr in cast-T6 conditions is characterized by an excellent creep resistance, which is higher than that of commercially available Mg-alloys. Creep resistance of as-cast, as-extruded and extruded-T5 alloy Mg-10Gd-3Y-0,4Zr is lower. Cavity nucleation is heavily affected by the amount of secondary phases on the grain boundaries and also by the initial grain size of the microstructure. After extrusion and in the extruded-T5 conditions creep cavitation was not observed, whereas in the as-cast and cast-T6 conditions creep cavitation occurred on the high fraction of grain boundaries.

Microstructure and Creep Properties of Casting Mg-8Al-0.3Mn Alloy Containing Ca and Sr

2011 ◽  
Vol 189-193 ◽  
pp. 1386-1392
Author(s):  
Yan Lou ◽  
Luo Xing Li
Keyword(s):  
Grain Boundaries ◽  
Creep Resistance ◽  
Elevated Temperatures ◽  
Secondary Phases ◽  
X Ray Diffraction ◽  
Creep Tests ◽  
Creep Properties ◽  
Calcium Addition ◽  
Order Of Magnitude ◽  
Cast Microstructure

Microstructures and creep properties of AM80 alloy with calcium and strontium additions have been investigated by using OM, X-ray diffraction, SEM and creep tests. The results indicate that the as-cast microstructure of the AM80 alloy consists of the α-Mg matrix, bones-shaped Mg17Al12 and lamellar second precipitation phase at grain boundaries. Calcium and strontium can refine the grain size and the secondary phases. Calcium addition results in the formation of a fishbone Al2Ca eutectic phase in AM80 alloy. With the increase of calcium, reticular Al2Ca phase distribute at the grain boundaries. The creep resistance of the AM80 alloy is significantly improved by a small amount of strontium and calcium addition due to the formation of a grain boundary network consisting of the high melting point Al2Ca phase. Microstructure observations performed on the sample after creep testing reveal that the phase is distorted during creep, reflecting its formation in the as-cast microstructure is unbeneficial to creep properties of the AM80 alloy. The creep resistance of the alloy at elevated temperatures was remarkably increased when calcium was added combined with strontium. The highest creep resistance was obtained from the alloy with xSr and y3Ca addition and its steady state creep rate reached as low as 3.941×10-8s-1, one order of magnitude lower than that of alloy AM80 without strontium and calcium additions.

The Creep Behaviors of Two Fine-grained XD TiAl Alloys Produced by Similar Heat Treatments

2004 ◽  
Vol 842 ◽  
Author(s):  
Hanliang Zhu ◽  
Dongyi Seo ◽  
Kouichi Maruyama ◽  
Peter Au
Keyword(s):  
Grain Boundaries ◽  
Creep Resistance ◽  
Lamellar Spacing ◽  
Heat Treatments ◽  
Tensile Creep ◽  
Microstructural Stability ◽  
Creep Tests ◽  
Tial Alloys ◽  
Fine Grained ◽  
Interlocked Grain

ABSTRACTThe microstructural characteristics and creep behavior of two fine-grained XD TiAl alloys, Ti-45Al and 47Al–2Nb–2Mn+0.8vol%TiB2 (at%), were investigated. A nearly lamellar structure (NL) and two kinds of fully lamellar (FL) structures in both alloys were prepared by selected heat treatments. The results of microstructural examination and tensile creep tests indicate that the 45XD alloy with a NL structure possesses an inferior creep resistance due to its coarse lamellar spacing and larger amount of equiaxed γ grains at the grain boundaries, whereas the same alloy in a FL condition with fine lamellar spacing lowers the minimum creep rates. Contrary to 45XD, the 47XD alloy with a NL structure exhibits the best creep resistance. However, 47XD with a FL structure with finer lamellar spacing shows inferior creep resistance. On the basis of microstructural deformation characteristics, it is suggested that the well-interlocked grain boundary and relatively coarse colony size in FL and NL 47XD inhibit sliding and microstructural degradation at the grain boundaries during creep deformation, resulting in better creep resistance. Therefore, good microstructural stability is essential for improving the creep resistance of these alloys.

The role of intergranular precipitates in controlling creep cavitation

1980 ◽  
Vol 295 (1413) ◽  
pp. 307-307
Keyword(s):  
Surface Energy ◽  
Tensile Stress ◽  
Grain Boundaries ◽  
Stress Axis ◽  
Creep Cavitation ◽  
High Fraction ◽  
Work Done ◽  
Applied Stresses ◽  
Small Obstacle ◽  
Applied Tensile Stress

A satisfactory model for cavitational failure in creep must account for the fact that fracture can occur under a very low stress, for example, only 0.7 MPa for a solid solution magnesium alloy. A mechanism for growth based on the transfer of vacancies from high angle grain boundaries to intergranular cavities satisfies this low stress requirement for it converts a relatively high fraction of the work done by the applied load into surface energy of fracture. However, for such growth to proceed, cavity nuclei of radius greater than a critical value, r c , must exist on those grain boundaries which are approximately normal to the applied tensile stress axis. It can be shown quite simply that r c = 2y/o, where y is the surface energy per unit area and o the applied tensile stress. A typical value for r c is 1 pm which is far too large to occur spontaneously by chance accumulation of vacancies. It is in fact generally agreed that cohesion is lost owing to the concentration of stress at some small obstacle in a sliding grain boundary. These cavities are nucleated along the boundary under applied stresses which are lower than those needed to cause triple point cracking where the whole of the length of the boundary is available to concentrate stress. This was a puzzle until Smith & Barnby (1967) demonstrated that the stress concentrated at a small obstacle in a sliding boundary was far higher than that concentrated at a very large obstacle as incorporated in, for example, the Stroh derivation.

Effect of Cold Plastic Deformation Prior to Ageing on Creep Resistance of an Al-Cu-Mg-Ag Alloy

2014 ◽  
Vol 794-796 ◽  
pp. 278-283 ◽  
Author(s):  
Marat Gazizov ◽  
Ivan Zuiko ◽  
Rustam Kaibyshev
Keyword(s):  
Creep Resistance ◽  
Diffusion Processes ◽  
Thermomechanical Processing ◽  
High Strength ◽  
Strain Effect ◽  
Cold Plastic Deformation ◽  
Secondary Phases ◽  
Ω Phase ◽  
Phase Plates ◽  
Minimal Creep Rate

Effect of thermomechanical processing on creep resistance at 150°C of an Al-5.6Cu-0.72Mg-0.5Ag-0.32Mn-0.17Sc-0.12Zr (wt. %) alloy was examined. It was shown that increasing strain prior to artificial aging provides achieving high strength. However, a degradation of the creep resistance, i.e., significant decrease in the rupture time and increase in the minimal creep rate, took place, concurrently. The effect of cold rolling on the strength and creep resistance is discussed in relation with the strain effect on the dispersion of secondary phases. The increase in strength and degradation of creep properties of the alloy subjected to cold working before ageing result from superposition of two competitive processes. First, an increase in the lattice dislocation density facilitates the precipitation of Ω-phase plates with high aspect ratio, leading to increase in the static strength at room temperature. Second, acceleration of the diffusion processes results in coarsening of strengthening phase in grain/subgrain interiors and precipitation of Ω-phase on deformation-induced boundaries during creep that deteriorates creep resistance.

An Experimental and Modeling Investigation of Tensile Creep Resistance in a Stable Nanocrystalline Alloy

2020 ◽  
Author(s):  
C. Kale ◽  
S. Srinivasan ◽  
B.C. Hornbuckle ◽  
R.K. Koju ◽  
K. Darling ◽  
...  
Keyword(s):  
Creep Resistance ◽  
Nanocrystalline Alloy ◽  
Tensile Creep

scholarly journals Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy

2020 ◽  
Vol 39 (1) ◽  
pp. 136-145 ◽  
Author(s):  
Sojiro Uemura ◽  
Shiho Yamamoto Kamata ◽  
Kyosuke Yoshimi ◽  
Sadahiro Tsurekawa
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Grain Boundary Sliding ◽  
Primary Creep ◽  
Tensile Creep ◽  
Tertiary Creep ◽  
Continuous Dynamic Recrystallization ◽  
Continuous Dynamic ◽  
Creep Regime

AbstractMicrostructural evolution in the TiC-reinforced Mo–Si–B-based alloy during tensile creep deformation at 1,500°C and 137 MPa was investigated via scanning electron microscope-backscattered electron diffraction (SEM-EBSD) observations. The creep curve of this alloy displayed no clear steady state but was dominated by the tertiary creep regime. The grain size of the Moss phase increased in the primary creep regime. However, the grain size of the Moss phase was found to remarkably decrease to <10 µm with increasing creep strain in the tertiary creep regime. The EBSD observations revealed that the refinement of the Moss phase occurred by continuous dynamic recrystallization including the transformation of low-angle grain boundaries to high-angle grain boundaries. Accordingly, the deformation of this alloy is most likely to be governed by the grain boundary sliding and the rearrangement of Moss grains such as superplasticity in the tertiary creep regime. In addition, the refinement of the Moss grains surrounding large plate-like T2 grains caused the rotation of their surfaces parallel to the loading axis and consequently the cavitation preferentially occurred at the interphases between the end of the rotated T2 grains and the Moss grains.

scholarly journals Processing of Bi–Sr–Ca–Cu–O glasses using platinum and alumina crucibles

1992 ◽  
Vol 7 (8) ◽  
pp. 2035-2039 ◽  
Author(s):  
T.G. Holesinger ◽  
D.J. Miller ◽  
S. Fleshler ◽  
L.S. Chumbley
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Grain Boundaries ◽  
Annealed Sample ◽  
Substrate Material ◽  
Superconducting Phase ◽  
Transition Temperatures ◽  
Secondary Phases ◽  
Second Phases ◽  
Potential Substrate

Reactions with alumina and platinum crucibles were studied during the preparation of Bi2Sr2Ca1Cu2Oy “2212” glasses. In particular, reactions with Al2O3 are of interest since alumina is a potential substrate material in applications of this superconductor. Glasses processed using alumina crucibles were completely homogeneous and free of secondary phases although the material contained 2.26 at. % Al in solution. After heat treatments, Al was found in the form of SrCaAlOy particles located primarily along grain boundaries of the 2212 superconducting phase. Platinum contamination was minimal (<0.02 at. %) and no Pt-containing secondary phases were found in amorphous or annealed samples. Glasses made with Pt crucibles were found to contain small amounts of CaO, Sr14−xCaxCu24O41, and 2201 as second phases. Differential thermal analysis (DTA) suggested that the crystallization processes were essentially the same for all samples although the small amount of Al seemed to slow the kinetics leading to the formation of 2212. Neither Al nor Pt was detected within the 2212 phase. The measured superconducting compositions in each annealed sample were nearly the same with identical transition temperatures of 88 K. Overall differences in stoichiometry were accommodated by changes in the number and composition of the secondary phases present.

Atom probe tomographic study of elemental segregation at grain boundaries for a peak-aged Al–Zn–Mg alloy

2014 ◽  
Vol 79 ◽  
pp. 1-4 ◽  
Author(s):  
X.Y. Sun ◽  
B. Zhang ◽  
H.Q. Lin ◽  
Y. Zhou ◽  
L. Sun ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Atom Probe ◽  
Mg Alloy ◽  
Elemental Segregation ◽  
Peak Aged

Microstructure and Creep Properties of AJ62 and AE44 Die-Casting Magnesium Alloys

2010 ◽  
Vol 638-642 ◽  
pp. 1546-1551 ◽  
Author(s):  
Andrzej Kiełbus ◽  
Tomasz Rzychoń
Keyword(s):  
Magnesium Alloys ◽  
Creep Resistance ◽  
Cell Structure ◽  
Creep Behaviour ◽  
Die Casting ◽  
Tensile Creep ◽  
Creep Properties ◽  
Die Cast ◽  
Subgrain Formation ◽  
Good Creep Resistance

Microstructure and tensile creep behaviour of the die-cast AE44 and AJ62 magnesium alloys has been studied at temperatures between 175°C and 200°C and at stresses in the range from 60 to 75 MPa. At the 175°C the AJ62 and AE44 alloys exhibit good creep resistance after 120h creep deformation. At 200°C the AE44 alloy shows still good creep resistance, whereas in the case of AJ62 alloy the rapid decreasing of creep resistance has been observed. TEM observations reveal dislocations cell structure in AE44 alloy after creep test. In AJ62 alloy subgrain formation and decreasing the dislocation density have been observed.

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