High Temperature Brittleness of Cast Alloys / Kruchosc Wysokotemperaturowa Stopów Odlewniczych

2013 ◽  
Vol 58 (1) ◽  
pp. 83-87 ◽  
Author(s):  
I. Telejko ◽  
H. Adrian ◽  
B. Guzik
Keyword(s):  
Liquid Phase ◽  
Crack Nucleation ◽  
Marked Change ◽  
Crack Tip ◽  
Solidification Process ◽  
Diffusional Flux ◽  
Cast Alloys ◽  
Last Stage ◽  
Major Factors ◽  
Strength And Ductility

Over-all mechanical properties of alloys are extremely low at the last stage of solidification where alloy exists at brittle temperature range (BTR). When the solidification process is completed a sudden and marked change in strength and ductility of metal is observed. It means that as long as liquid phase is present, metal will fail in a brittle manner. There are known different theories of brittleness of alloys in existence of liquid phase. The idea involved by authors of the paper is as follows: three major factors caused by presence of liquid may be taken into account: - decreasing the energy needed for crack nucleation, - increasing atomic diffusional flux out of the crack tip, - creating a path for abnormally quick diffusion of atoms from the crack tip.

Effects of Si content on the microstructure and tensile strength of an in situAl/Mg2Si composite

1999 ◽  
Vol 14 (1) ◽  
pp. 68-74 ◽  
Author(s):  
Jian Zhang ◽  
Yu-qing Wang ◽  
Bing Yang ◽  
Ben-lian Zhou
Keyword(s):  
Tensile Strength ◽  
Metal Matrix ◽  
Die Casting ◽  
Solidification Process ◽  
Matrix Composites ◽  
Fracture Characteristics ◽  
Casting Technique ◽  
Si Content ◽  
Strength And Ductility

Al/Mg2Si composites were in situ fabricated by the usual die-casting technique, and effects of the Si contents in the composites on microstructures and tensile strengths were investigated. Experimental results show that extra Si contents in Al/Mg2Si composites induce a ductile matrix and a uniform distribution of in situ particles. The refined microstructures lead to an obvious increase in both strength and ductility of the metal matrix composites (MMCs). The effects of extra Si on both the solidification process and fracture characteristics of the Al/Mg2Si composites were analyzed.

DC Casting, Deformation and Strengthening of Al-Si Alloys

2012 ◽  
Vol 706-709 ◽  
pp. 186-193 ◽  
Author(s):  
Liang Zuo ◽  
Fu Xiao Yu
Keyword(s):  
Mechanical Properties ◽  
Direct Chill ◽  
Cast State ◽  
The Poor ◽  
Low Thermal Expansion ◽  
Cast Alloys ◽  
Superior Mechanical Properties ◽  
Deformation And Heat Treatment ◽  
Dc Casting ◽  
Strength And Ductility

Al-Si alloys are widely used as cast alloys for their excellent castability, low thermal expansion coefficient, good wear resistance and corrosion resistance properties. However, the poor ductility of these alloys, caused by the presence of coarse and non-deformable Si phase in the as-cast state, has inhibited their applications as wrought materials. Recently, a process based on traditional technologies, i.e., direct chill (DC) casting followed by hot deformation and heat treatment, has been developed for potential mass production of wrought Al-Si alloys with superior mechanical properties in view of their strength and ductility. In this work, the microstructural evolutions of DC cast Al-Si alloys involved in solidification, recrystallization and precipitation during the processing are highlighted, aiming at understanding the correlations between the microstructures and the mechanical properties.

Solidification of Al-Pb Alloy under the Effect of Micro-Alloying Element Ti and C

2016 ◽  
Vol 879 ◽  
pp. 2439-2443 ◽  
Author(s):  
Qian Sun ◽  
Hong Xiang Jiang ◽  
Jiu Zhou Zhao
Keyword(s):  
Phase Transformation ◽  
Liquid Phase ◽  
Microstructure Evolution ◽  
Solidification Process ◽  
Miscibility Gap ◽  
Kinetic Behavior ◽  
Number Density ◽  
Alloying Element ◽  
Refinement Efficiency ◽  
Line Temperature

Experiments were carried to investigate the effect of TiC on the solidification process and microstructure of Al-Pb alloys. It is demonstrated that TiC particles are effective inoculants for the nucleation of the Pb-rich droplets during cooling an Al-Pb alloy in the miscibility gap. A model describing the kinetic behavior of TiC particles in the melt and the liquid-liquid decomposition of Al-Pb was developed. The dissolution, coarsening and precipitation processes of TiC particles as well as the microstructure evolution during the liquid-liquid phase transformation of an Al-Pb alloy were calculated. The numerical results indicate that what determines the refinement efficiency of TiC particles on the Pb-rich droplets/particles is the number density of TiC particles in the melt cooled to the binodal line temperature of the Al-Pb alloy. If the number density of TiC particles in the melt before the beginning of the liquid-liquid decomposition is high enough, the addition of TiC causes a refinement of the Pb-rich droplets/particles and promotes the formation of Al-Pb alloys with a well dispersed microstructure.

Influence of Cooling Rate on the Size of the Precipitates and Thermal Characteristic of Al-Si Cast Alloys

2006 ◽  
Vol 15-17 ◽  
pp. 59-64 ◽  
Author(s):  
Rafal Maniara ◽  
Leszek Adam Dobrzański ◽  
Jerry Sokolowski ◽  
Wojciech Kasprzak ◽  
Witold T. Kierkus
Keyword(s):  
Cooling Rate ◽  
Solidus Temperature ◽  
Thermal Characteristic ◽  
Solidification Process ◽  
Crystallization Curve ◽  
Dendrite Coherency Point ◽  
Cast Alloys ◽  
Main Observation ◽  
Coherency Point ◽  
Work Effect

In this work effect of cooling rate on the size of the grains, SDAS, β phases and thermal characteristic results of Al-Si cast alloys have been described. The solidification process was studied using the cooling and crystallization curve at cooling rate ranging from 0,1 °Cs-1 up to 1 °Cs-1. The main observation made from this work was that when cooling rate is increased the aluminum dendrites nucleation temperature and solid fraction at the dendrite coherency point increases, which implies that mass feeding is extended. In addition to that, it was observed that solidus temperature and size of the β phases decreases when cooling rate increases. Investigations were showed, that the thermal modification could be quantitatively assessed by analysis of the crystallization curve.

scholarly journals The return of the dispersed metal waste into production

2019 ◽  
pp. 45-48
Author(s):  
S. L Rovin ◽  
A. S. Kalinichenko ◽  
L. E. Rovin
Keyword(s):  
Chemical Composition ◽  
Liquid Phase ◽  
Mill Scale ◽  
Metal Waste ◽  
Organic Impurities ◽  
Processing Wastes ◽  
Cast Alloys ◽  
Preliminary Preparation ◽  
Solid Liquid ◽  
Phase Process

The article presents an alternative method of recycling of dispersed metal waste, based on a continuous solid-liquid-phase process, implemented in rotary tilting furnaces (RTF). The new proposed method of recycling allows processing wastes with almost any composition and state from metal to oxide and multicomponent wastes (shavings, fine scrap, mill scale, aspiration dust, sludge, etc.). The wastes can be even contaminated with moisture, oil, and organic impurities. The method developed does not require preliminary preparation of the initial materials (cleaning, homogenization, pelletizing, etc.). The finished products are ingots (pigs) for subsequent processing aiming the particular chemical composition or cast alloys of certain brend.

Controlled Initiation of Short Fatigue Cracks in 316L Steel

2005 ◽  
Author(s):  
D. Stefanescu ◽  
J. Marrow ◽  
M. Preuss ◽  
A. Sherry
Keyword(s):  
Experimental Study ◽  
Stainless Steel ◽  
Crack Opening Displacement ◽  
Crack Nucleation ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Crack Tip ◽  
Image Correlation ◽  
Opening Displacement ◽  
R Ratio

Validation of models for short crack behavior requires accurate measurement of crack opening displacement and crack tip strain fields. Development of reliable measurement procedures, using new techniques such as Image Correlation (IC), requires specimens containing cracks with a well defined geometry. In this paper, results of an experimental study concerning controlled initiation of short fatigue cracks at positive R-ratio in laboratory specimens made from 316L stainless steel are presented. Experimental techniques, including hardness testing and X-ray diffraction were employed in order to investigate the effect of surface preparation on the surface mechanical properties and residual stresses. Crack nucleation is difficult in smooth specimens of 316L austenitic stainless steel at positive R-ratio due to the high fatigue limit and low tensile strength. Specimens with a thin ligament were therefore developed to enable nucleation of a single short fatigue crack. An experimental study of the crack growth aspect ratio evolution was then carried out using a beach marking technique. The technique described in this paper enables single short fatigue cracks of well defined geometry to be nucleated under tensile cyclic loading. Stress corrosion cracks can be developed using the same specimen geometry. Miniature tensile specimens can then be extracted to perform in-situ measurements of the crack opening displacement and crack tip strain field by Image Correlation from Scanning Electron Microscopy observations.

scholarly journals Niobium Additions to a 15%Cr–3%C White Iron and Its Effects on the Microstructure and on Abrasive Wear Behavior

Metals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1321 ◽  
Author(s):  
Arnoldo Bedolla-Jacuinde ◽  
Francisco Guerra ◽  
Ignacio Mejia ◽  
Uzzi Vera
Keyword(s):  
Heat Treatment ◽  
Wear Resistance ◽  
Abrasive Wear ◽  
Volume Fraction ◽  
Wear Behavior ◽  
Solidification Process ◽  
White Iron ◽  
Bulk Hardness ◽  
Abrasive Wear Behavior ◽  
Cast Alloys

From the present study, niobium additions of 1.79% and 3.98% were added to a 15% Cr–3% C white iron, and their effects on the microstructure, hardness and abrasive wear were analyzed. The experimental irons were melted in an open induction furnace and cast into sand molds to obtain bars of 45 mm diameter. The alloys were characterized by optical and electron microscopy, and X-ray diffraction. Bulk hardness was measured in the as-cast conditions and after a destabilization heat treatment at 900 °C for 30 min. Abrasive wear resistance tests were undertaken for the different irons according to the ASTM G65 standard in both as-cast and heat-treated conditions under three loads (58, 75 and 93 N). The results show that niobium additions caused a decrease in the carbon content in the alloy and that some carbon is also consumed by forming niobium carbides at the beginning of the solidification process; thus decreasing the eutectic M7C3 carbide volume fraction (CVF) from 30% for the base iron to 24% for the iron with 3.98% Nb. However, the overall carbide content was constant at 30%; bulk hardness changed from 48 to 55 hardness Rockwell C (HRC) and the wear resistance was found to have an interesting behavior. At the lowest load, wear resistance for the base iron was 50% lower than that for the 3.98% Nb iron, which is attributed to the presence of hard NbC. However, at the highest load, the wear behavior was quite similar for all the irons, and it was attributed to a severe carbide cracking phenomenon, particularly in the as-cast alloys. After the destabilization heat treatment, the wear resistance was higher for the 3.98% Nb iron at any load; however, at the highest load, not much difference in wear resistance was observed. Such a behavior is discussed in terms of the carbide volume fraction (CVF), the amount of niobium carbides, the amount of martensite/austenite in matrix and the amount of secondary carbides precipitated during the destabilization heat treatment.

Effect of Magnesium and Artificial Aging on the Microstructure and Mechanical Properties of Al-Si-Mn-Mg Alloys

2009 ◽  
Vol 83-86 ◽  
pp. 415-420
Author(s):  
S.G. Shabestari ◽  
M.M. Hejazi ◽  
M. Bahramifar
Keyword(s):  
Mechanical Properties ◽  
Quality Index ◽  
Industrial Applications ◽  
Maximum Value ◽  
Microstructure And Mechanical Properties ◽  
Heat Treated ◽  
Cast Alloys ◽  
Mg Addition ◽  
Strength And Ductility ◽  
Magnesium Addition

The effect of magnesium addition up to 0.9 wt.% on the microstructure and mechanical properties of Al-9Si-0.35Mn alloy has been investigated in both as-cast and heat treated conditions. Generally, Mg addition increases the heat treatability and strength of the alloys at the expense of the lower ductility. High levels of magnesium addition, causes the formation of large and brittle intermetallics, a slight increase in porosity and hence, a decrease in ultimate tensile strength and ductility of the cast alloys. T6 heat treatment increases the strength of the alloys up to 80 percent compared to as-cast samples. Among the studied compositions, heat treated Al-9Si-0.35Mn-0.25Mg alloy, has the maximum value of quality index and can be regarded as a promising material with the optimum mechanical properties for industrial applications.

scholarly journals The Evolution of Microstructure, Mechanical Properties and Fracture Behavior with Increasing Lanthanum Content in AZ91 Alloy

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1256
Author(s):  
Di Tie ◽  
Yi Jiang ◽  
Renguo Guan ◽  
Minfang Chen ◽  
Jufu Jiang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Behavior ◽  
Aging Treatment ◽  
Industrial Applications ◽  
Az91 Alloy ◽  
Refined Microstructure ◽  
Lanthanum Content ◽  
Cast Alloys ◽  
Evolution Of Microstructure ◽  
Strength And Ductility

AZ91 alloy is a widely applied commercial magnesium alloy due to its good castability, balanced mechanical properties and acceptable price, and lanthanum alloying has been proven to be one of the most effective methods to further improve its mechanical properties. Therefore, we reveal the evolution of microstructure, mechanical properties and fracture behavior with increasing lanthanum content in AZ91 alloy in this study. The magnesium matrix was significantly refined by lanthanum content, and this effect became more evident with increasing addition of lanthanum. The presence of Al3La precipitates significantly reduced the grain mobility and suppressed the formation of Mg17Al12 discontinuous precipitates along the grain boundaries. The rheo-cast alloys exhibited improved and balanced tensile strength and ductility after aging treatment. The fracture type of AZ91-La alloys could be classified as ductile fracture due to the presence of less quasi-cleavage planes and more dimples with a mixture of tear ridges and micropores. Due to the fully refined microstructure and the balanced mechanical properties, the AZ91–1.0La (mass%) alloy presented the greatest potential for industrial applications among the three studied AZ91-La alloys.

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