Influence Of Cooling Rate Research Articles

Influence of Cooling Rate on the Hot Cracking Formation of Nickel Rich Alloys.

Hot cracking formation and its mechanism in invar alloys (Fe–36mass%Ni) during continuous casting was investigated. The invar alloy is very sensitive to hot cracking due to its low transition temperature of brittle to ductile fracture even though its solidification interval is narrow. At the cooling rate of 10°C/min the transition temperature of brittle to ductile fracture is about 113°C below the solidus temperature. An increased cooling rate in invar alloy increases transition temperature of brittle to ductile fracture. It is increased to about 43°C below the solidus temperature when the cooling rate is increased to 100°C/min. A mechanism of hot cracking formation in invar alloys has been proposed. Hot cracks in invar alloys with a fast cooling rate are formed between the primary dendrites due to the equiaxed solidification structure. However, at slow cooling rate, hot cracks are formed between the grain boundaries due to the columnar structure.

Influence of Cooling Rates and Plunging Temperatures in an Interrupted Slow-Freezing Procedure for Semen of the African Catfish, Clarias gariepinus

The objective of this study was to optimize interrupted slow-freezing protocols for African catfish semen. Semen diluted with methanol and extender was frozen in 1-ml vials in a programmable freezer. The temperatures of the freezer (Tchamber) and of the semen (Tsemen) were measured simultaneously. We first tested two-step freezing protocols with different cooling rates (−2, −5, and −10°C/min) and different temperatures at plunging into liquid N2. The difference between Tsemen and Tchamber increased with faster cooling rates. In all programs, survival of spermatozoa, expressed as hatching rates, increased from near zero when Tsemen at plunging was higher than −30°C to values equal to those of control when Tsemen at plunging was equal to or lower than −38°C. The inclusion of an isothermal holding period before plunging into liquid N2 (three-step freezing protocols) resulted in an equilibration between Tsemen and Tchamber and improved semen survival. Semen could be plunged at temperatures as high as −36°C when cooled at −5 or −10°C/min, without compromising postthaw semen survival. Cooling at −2°C/min in combination with a 5-min holding period reduced postthaw survival. We conclude that with slow cooling rates of −2 to −5°C/min, hatching rates can be maximized by plunging as soon as Tsemen reaches −38°C. The isothermal holding period is beneficial when faster rates are used. A simple and efficient protocol for freezing African catfish semen can be obtained by cooling at a rate of −5 to −10°C/min combined with a 5-min holding period in the freezer, at −40°C

An analysis of cooling rate influence on the sequence of intermetallic phases precipitation in some commercial aluminium alloys

M. Warmuzek and A. Gazda, J. Anal. At. Spectrom., 1999, 14, 535 DOI: 10.1039/A808100J

Influence of Cooling Rate After Baking on Crack of CTL in Preparing of Organic Photoconductor

Influence of Cooling Rate After Baking on Crack of CTL in Preparing of Organic Photoconductor

Influence of Cooling Rate on Fatigue Reliability of Austempered Ductile Iron.

The influence of cooling rate on the fatigue reliability of austempered ductile iron (ADI) was investigated with special attention given to a mesoscopic factor of fracture origin. The main results were as follows. (1) The fatigue strength of ADI could be improved by increasing the cooling rate. (2) Different kinds of casting defects were observed at the origin of fatigue crack in three types of ADI, which were produced through rapid, medium and slow cooling rates (designated as R, M and S materials, respectively). These are larger dross, spheroidal graphite and porosity in R, M and S materials, respectively. (3) The mesoscopic factors of fracture origin, which consisted of casting defects and matrix microstructure, could be quantitatively related to the fatigue life.

An Influence of Cooling Rate on the Fatigue Reliability of Metal-Molded Aluminum Alloy Castings.

An influence of cooling rate on the fatigue reliability of aluminum alloy castings (AC4CH) was investigated. The results obtained were as follows : (1) As the cooling rate of AC4CH was increased, the porosities and the microstructure were controlled fine. (2) The fatigue strength of AC4CH produced through rapid cooling rate was superior to that produced through slow cooling rate, specially on the fatigue limit (N=107). (3) The effect of stress gradient on the fatigue limit is due to the probability that the maximum stress can put on the largest porosity in the specimen. (4) Micro porous defects were always observed at the origin of fatigue crack. Then, it could be interpreted that the fatigue life was related to the size of porous defect, based on fracture mechanics. (5) From the above relation and the statistical analysis on the size of porous defect, the fatigue limit of 99% remaining probability could be estimated.

Influence of Cooling Rate on Outgrowth of Clostridium perfringens Spores in Cooked Ground Beef

The ability of Clostridium perfringens spores to germinate and grow was studied to determine a safe cooling rate for cooked beef. Beef samples were inoculated with a cocktail of three strains of heat-shocked C. perfringens spores (NCTC 8238, NCTC 8239 and ATCC 10288), vacuum-packaged, and cooked in a stirred water bath to an internal temperature of 60°C in 1 h. Then, samples were cooled through the temperature range of 54.4°C to 7.2°C at rates varying from 6 to 18 h. Samples were removed at various times during cooling to determine if the spores had germinated and multiplied. The samples were plated on tryptose-sulfite-cycloserine agar and incubated anaerobically at 37°C for 48 h. Minimal growth was observed with cooling periods of up to 15 h. However, with the time to achieve 7.2°C extended to 18 h, C. perfringens spores germinated and grew from an inoculum of approximately 1.5 log10 to about 6.0 log10 CFU/g. This study indicated that pasteurized cooked beef must be cooled to 72°C in 15 h or less to prevent C. perfringens foodborne disease outbreaks.

Influence of Cooling Rate on Electrical Properties of Zinc Oxide-Based Varistors

The influence of the cooling rate on the microstructure, the nonlinear parameter α, the breakdown voltage V1mA/cm2, the dielectric properties and the leakage current of the ZnO varistors was investigated. The morphology of the microstructure has different appearances under the effect of the varying cooling rates. The nonlinear parameter and the breakdown voltage reached a maximum as the cooling rate was adequately chosen. In the frequency range of 600∼1 MHz, the dielectric properties of the samples dealt with at different cooling rates showed a similar tendency. However, the leakage currents of the samples showed different behavior under a constant voltage stress. As a result, the physical and electrical properties of the ZnO varistors can be said to be affected by the cooling rate.

Influence of contraction mismatch and cooling rate on flexural failure of PFM systems.

The interactive influence of cooling rate and the sign and magnitude of thermal contraction difference between metals and ceramic veneers on bond strength have not been extensively analyzed, although numerous bond-test studies have been reported during the past two decades. A previous analytical study of residual incompatibility stress in bond-test specimens indicated that bond strength values may be of relatively little value if the residual stress state of the metal-ceramic specimens is not considered. The objective of this study was to determine the influence of cooling rate and contraction mismatch on the flexural failure resistance of metal opaque-porcelain strips. Specimens were subjected to four-point loading in an Instron testing machine until crack initiation occurred at the metal-ceramic interface. The residual stress states in the ceramic region were estimated from finite element stress analyses of the bond-test specimens by use of dilatometry data obtained at the cooling rate of 3 degrees C/min. The total stress induced from the residual stress and the applied flexural load was also determined for these specimens. Statistical analyses of the experimental data revealed that the slowly cooled specimens exhibited a significantly lower (p < 0.05) flexural strength compared with rapidly cooled specimens. Regardless of the cooling technique, metal-ceramic specimens with a negative thermal contraction difference (alpha m - alpha p < 0) failed at significantly lower (p < 0.05) flexural loads than did specimens with a positive thermal contraction difference.

Influence of cooling rates and extenders upon post-thaw viability of bovine spermatozoa packaged in .25- and .5-ml French straws.

Post-thaw survival of bovine spermatozoa was compared for semen packaged in either .25- or .5-ml French straws and frozen at three different cooling rates in moving N2 vapor. Using a split ejaculate technique, nine ejaculates were extended in heated skim milk, egg yolk-citrate and egg yolk-Tris and packaged in .25- and .5-ml French straws. Semen packaged in the .25- and .5-ml straws was frozen simultaneously at initial N2 vapor temperatures of -140, -110 or -80 C. Semen was thawed in a water bath at 35 C for 1 min. Recovery of spermatozoa was evaluated immediately post-thaw (0 h) and again after 3 h of incubation at 37 C. Motility estimates and motility counts were made using phase contrast microscopy; percentage of spermatozoa possessing intact acrosomes was quantitated using differential interference contrast microscopy. There was a packaging unit X cooling rate interaction (P less than .05) for all three viability measures. However, there was no consistent trend with regard to cooling rate or packaging unit among the three extenders examined. Post-thaw viability for each characteristic varied (P less than .01) among extenders, but not for cooling rate or packaging unit (P greater than .05). Spermatozoa extended and frozen in egg yolk-Tris had greater (P less than .05) post-thaw viability than those extended in skim milk or egg yolk-citrate regardless of cooling rate or volume of the seminal package.

Influence of Cooling Rate on the Mechanical Strength and Eutectic Cell Structure of Cylindrical Gray Cast Iron

Influence of Cooling Rate on the Mechanical Strength and Eutectic Cell Structure of Cylindrical Gray Cast Iron

Influence of Cooling Rate on Quantity and Behavior of AlN in Fe-C-Si-Al Alloy Melt

Influence of Cooling Rate on Quantity and Behavior of AlN in Fe-C-Si-Al Alloy Melt

The Influence of Cooling Rate on the Mechanical Strength and Eutectic Cell Structure of Plate Iron Castings

The Influence of Cooling Rate on the Mechanical Strength and Eutectic Cell Structure of Plate Iron Castings

Influences of Cooling Rate, Mass Effect, Mn/S Content Ratio and Ca-Si Inoculation on the Formation of &ldquo;As Cast&rdquo; Ferritie Matrix of Spheroidal Graphite Cast Iron

Influences of Cooling Rate, Mass Effect, Mn/S Content Ratio and Ca-Si Inoculation on the Formation of &ldquo;As Cast&rdquo; Ferritie Matrix of Spheroidal Graphite Cast Iron

Influence of Cooling Rate on Ferrite Formation in Cast Iron

Influence of Cooling Rate on Ferrite Formation in Cast Iron

Influences of Cooling Rate, Silicon Content and Mn/S Ratio on the Formation of As-Cast Ferritic Matrix of Spheroidal Graphite Cast Iron

Influences of Cooling Rate, Silicon Content and Mn/S Ratio on the Formation of As-Cast Ferritic Matrix of Spheroidal Graphite Cast Iron

Influence of Cooling Rate on the Structure of Ferritic Cast Iron

Influence of Cooling Rate on the Structure of Ferritic Cast Iron

Influence of Cooling Rate and Composition on Intergranular Fracture of Cast Steel

AbstractIn heavy steel castings, especially high-strength quenched and tempered castings, inter granular brittleness presents a major problem. Earlier investigations have shown this to depend on the precipitation of a thin brittle phase in the primary grain boundaries. If the embrittling phase is A1N, three variables will control the precipitation; aluminium content of the steel, nitrogen content, and cooling rate. Slow cooling rates and large alloy contents promote precipitation. The paper shows how to calculate the thickness of the precipitate on continuous cooling and thus to assess the risk of intergranular fracture. Two solutions are presented, an approximate one based on the computed TTT diagram, and a more exact model in which the precipitation rate is integrated over the temperature range. The two solutions give reasonably similar results, thus proving the value of isothermal diagrams even in the case of continuous cooling.