The effect of TiO2 nanoparticles on fluid quenching characteristics

Abstract

Nanofluids are colloidal suspensions of nanoparticles in base fluids. Some of the particles used in recent research are metal oxide and carbide particles, such as SiC, CuO, Al₂O₃ and TiO₂, graphite and carbon nanotubes and particles. Quenching in such colloids results in better cooling abilities, higher impact toughness and smaller dimension changes of steels, compared with pure quenching media. In this investigation, nanofluids with TiO₂ powders of 50 nm average particle size were investigated. Base fluids of primary interest were deionised (DI) water, some commercial quenching oils and polyalkylene glycol water solution of various polymer concentrations, 5–30 vol.-%. The investigated fluids were prepared with the addition of the same TiO₂ powder with different concentrations, from extremely low, 10 mg nanopowder per litre to 1 g L^?1. The cooling characteristics of these colloids were compared with the results of base fluids, but also with the results of previous measurements carried out on the fluids with addition of Al₂O₃ micrometre and submicrometre size particles. All of the cooling curves were measured and recorded by the IVF Smart Quench system using a stainless steel probe of 12·5 mm diameter in accordance with ISO 9950 standard. The cooling rate (CR) versus temperature and time was compared for all of the investigated media. The preparation of fluids was conducted with great care, with respect to mechanical stirring and sonification times. The average particle size was measured for each case. In order to better understand the phenomena that occur during the quenching process, a high speed camera was used for recording the experiments. Titanium oxide nanoparticles show the most significant effects on the cooling properties of the water based polymer solution. The maximum cooling rate increases with higher particle concentration. When comparing the results of experiments with alumina particles, smaller and thermally less conductive TiO₂ particles show greater effects on nanofluid properties.     

Optimization of microstructure at Ni-C steel joint by friction stir welding with CO2 cooling

The effect of additional cooling by splaying liquid CO₂ during friction stir welding (FSW) on the microstructure change in the stir zone of Fe – 24 wt%Ni – 0.1%C alloy steel was investigated. When the cooling rate after the stirring increased by the adoption of a faster welding speed and the use of CO₂ cooling, a larger amount of retained austenite with lath martensite was present in the stir zone. The room temperature tensile test clarified that the retained austenite contributes to the high strength without loss of elongation due to the transformation-induced plasticity (TRIP) effect.     

Thermal flow simulation and visualisation of PAG quenchants in cooling evaluation equipment with twin stir

Abstract

In this research, the formation and movement of bubbles in boiling film during quenching process was investigated with high speed video camera and particle image velocimetry (PIV) technology as the visualisation method. Cooling curves of surface temperature during quenching of a silver cylinder were measured and the heat transfer coefficients between quenchant and quenching parts were identified. The cooling ability of the coolant used for the quenching technology was evaluated relative to the quality the machine part. As for this paper, the cooling capacity of the PAG quenchants (polyalkylene glycol solutions) was evaluated. In addition, the heat transfer behaviour in the quenching process is clarified with regard to the generation and the destruction of the thermal flow and collapse of the steam film by using the PIV method of visualisation. The effect of mechanical stirring of the quenchant on the steam film and heat transfer is also studied.     

Structure formation and properties of rapidly quenched aluminum alloys

Aluminum alloys in a rapidly quenched state are studied by four technological methods, namely, fabricating foils and wire with unique properties, fabricating granulated alloys, surface strengthening and alloying articles by a laser or an electron beam treatment, and realizing superplasticity. In rapid quenching of alloys, crystallization occurs with cooling the melt at a rate of at least 10³–10⁴ K/sec. Such cooling can be realized in practice by several methods, for example, by drop crystallization on a rotating heat-conducting substrate, spraying of the melt in a cooling medium, quenching a thin foil on cooled rolls in liquid rolling, or melting a thin surface zone of a quite massive part. The present paper describes a study of flakes of aluminum alloys obtained by the method of drop crystallization. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 31–34, May, 1997.     

Intensification of the quenching process in steel

Conclusions To reduce the possibility of quenching cracks and warping, the temperature of the boiling layer during intensive cooling of steel parts in cold liquid media should be equal to M_S or close to it. This can be achieved with additives or by increasing the pressure.Institute of Technical Thermophysics of the Academy of Sciences of the Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 64–65, February, 1970.     

An investigation on quench cracking behavior of superalloy udimet 720LI using a fracture mechanics approach

Quench cracking can be a serious problem in the heat treatment of high strength superalloys. A new fracture mechanics approach, quench cracking toughness (K _Q ), was introduced to evaluate the on-cooling quench cracking resistance of superalloy Udimet 720LI. A fully automatic computer controlled data acquisition and processing system was set up to track the on-cooling quenching process and to simulate the quench cracking. The influences of grain size, cooling rate, solution temperature, and alloy processing routes on quench cracking resistance were investigated. Research results indicate that quench cracking revealed a typical brittle and intergranular failure at high temperatures, which causes a lower quench cracking toughness in comparison to fracture toughness at room temperature. Fine grain structures show the higher quench cracking resistance and lower failure temperatures than intermediate grain structures at the same cooling rates. Moreover, higher cooling rate results in lower cracking toughness under the same grain size structures. In comparison of processing routes, powder metallurgy (PM) alloys show higher cracking resistance than cast and wrought (CW) alloys for fine grain structures at the same cooling rates. However, for intermediate grain structure, there is no obvious difference of K _Q between the two processing routes in this study.     

Q890高强钢焊接淬硬倾向和冷裂纹敏感性

通过焊接热模拟试验、焊接热影响区最高硬度试验以及公式计算,分析了Q890钢的焊接淬硬倾向和冷裂纹敏感性.结果表明,稻垣道夫建立的经验公式比D·Vwer建立的理论经验公式更适用于计算厚板的焊接冷却时间t8/5.Q890钢焊接热影响区的粗晶区具有较强的淬硬倾向,调整焊前预热温度以及焊接热输入,对Q890钢热影响区的淬硬倾向无明显改善,但焊前预热能有效增大冷却时间t100,降低试验钢的焊接冷裂倾向.通过计算机拟合建立了冷却时间ts/5与焊接热影响区过热区硬度的关系式,经过验证该关系式能够对Q890钢最高硬度进行合理的预测.     

Columnar to equiaxed transition during growth of a univariant eutectic

Abstract

In this work the transition from columnar to equiaxed growth is studied during the solidification of the univariant eutectic L→ α(Al) + θ-Al₂Cu in the ternary Al–Cu–Ag system. The experimental technique used is upwards solidification with a controlled cooling rate. In the lower part of the sample where the temperature gradient is high, a cellular eutectic is observed. When the temperature gradient decreases, the morphology first changes into two-phase dendrites and finally into an equiaxed eutectic. When the amount of Ag is increased, the formation of eutectic colonies becomes easier. Also, a higher cooling rate facilitates the formation of eutectic colonies. The addition of TiB₂ does not influence the nucleation of eutectic colonies. Although the composition is on the eutectic groove, primary α(Al)-dendrites are found in the samples with TiB₂. This leads to segregation effects due to the density difference between α(Al) and the liquid.     

Fast etching of copper in thionyl chloride/acetonitrile solutions

We report fast etching of copper (Cu) in thionyl chloride (SOCl₂)/acetonitrile (CH₃CN) solutions. The etching rate can be tuned over a wide range by varying the concentration of the etchant, and the stirring rate of the liquid. The etching rate reaches 36 mg min⁻¹ cm⁻² in 1 mol L⁻¹ SOCl₂/CH₃CN under stirring at room temperature, which is much faster than any currently used etchant for Cu. With sonication, the etching rate reaches 320 mg min⁻¹ cm⁻². The chemical reactions involved are studied by X-ray photoelectron spectroscopy and Raman spectroscopy. The fast etching may find important applications in microelectronics.     

Current research in Egypt on optimisation of combined mechanical strength and corrosion behaviour of steel rebar

Abstract

The effect of accelerated water cooling on the mechanical and corrosion properties of steel rebars produced from steel with composition of 0·17–0·286%C, 0·62–0·72%Mn, 0·15–0·20%Si has been assessed. The bars were rolled from continuously cast steel billets to 12, 16, 20 and 25 mm diameter. Immediately after the last rolling stand the steel bars entered the quenching box. Cooling conditions were varied by changing the number of cooling nozzles and the water flowrate. Initial bar temperature and equalised temperature were calculated using a mathematical model and recorded by pyrometers at the entry of the quenching box and the entry of the cooling bed. Corrosion resistance was determined potentiodynamically and by immersion tests in NaCl and Ca(OH)₂ solution. Equalising temperature decreased with increasing cooling time and water flowrate. Yield strength and ultimate tensile strength (UTS) increased and elongation decreased with decreasing equalising temperature, indicating that different steel grades can be obtained from billet of the same composition using accelerated cooling. Though no direct relationship was observed between mechanical properties and corrosion resistance, the results indicate that cooling conditions and process parameters for thermomechanical treatment should be selected on the basis of corrosion requirements as well as to produce the desired mechanical properties.     

对自来水作为淬火介质的两大缺点的研究

从自来水淬火时工件容易淬裂、硬度不均且畸变大等现象，列出了自来水作为淬火介质的两大缺点：一是低温冷却速度太快，二是冷却特性对水温变化太敏感。分析了自来水第二大缺点引起淬火硬度不均和畸变的原因。通过与气态介质的对比，指出了液态淬火介质共同的两类缺点：一是任何确定的液态介质，其冷却速度的可调节范围都很有限，以致同一个车间必须配备普通淬火油、中速淬火油和高速淬火油，才能满足不同工件的需要；二是工件从蒸汽膜阶段到沸腾阶段期间，冷却速度突然增大，可能引起较大的淬火畸变。提供了克服液态淬火介质第二类缺点的七类技术方法。     

6063铝合金的TTP曲线与淬火敏感性

采用中断淬火技术测定了6063铝合金的时间-温度-性能(TTP)曲线,透射电镜研究了6063铝合金的淬火敏感性.结果表明,6063铝合金的淬火敏感性低于6061和6082铝合金的,合金的鼻尖温度为360℃,淬火敏感区间为300～410℃.微观组织观察表明,在敏感区间内,β-Mg2Si平衡相优先在(AlxFeySiz)相上非均匀形核而析出,且在360℃鼻尖温度时的长大速度最快.平衡相的析出导致合金溶质原子的浓度下降,减少了时效时的β"强化相的数量,降低了强化效果.因此,对于6063铝合金大型材的淬火,一方面,在淬火敏感区间(410～300℃)应加大冷却速率以抑制平衡相的析出,从而获得较佳的时效强化效果;另一方面,适当减小从固溶温度到410℃以及低于300℃时的冷却速率,从而减小淬火应力.     

Effect of annealing and heating/cooling rate on the transformation temperatures of NiFeGa alloy

In this work, Ni₅₅Fe₁₈Ga₂₇ ferromagnetic shape memory alloy was prepared through a suck-casting method. The effects of annealing and heating/cooling rate on the martensitic transformation temperatures were investigated by differential scanning calorimetry (DSC). The results showed that the phase transformation temperatures increase with increasing the annealing temperature, upon the heating and cooling process. However, the start and the finish temperatures (M_s and M_f) of martensitic phase transformation increased firstly and then decreased upon the cooling process with the increase the annealing time at 300 °C. The start and the finish temperatures (A_s and A_f) of inverse phase transformation increased slightly upon the heating process with the increase of the annealing time. The results can be explained by the evolution of the microstructure after heat treatment. It was also found that the phase temperatures show great dependence on the heating/cooling rate of the DSC test, A_s and A_f increased and M_s and M_f decreased with the increase of the heating/cooling rate.     

Improvement of the liquid segregation phenomena of semisolid aluminum alloys by the multistage strain rate control in the compression test

The deformation behavior of semisolid aluminum alloys in the range of solid fraction (f _s ) between 55 and 90% was investigated through compression tests for the variation of strain rate. In order to obtain the optimal conditions of the net shape forging process, the rheological behavior of aluminum alloy in the semisolid state has been examined by using parallel plate compression. The strain rate is the value of the strain rate corresponding to the stress to avoid the liquid segregation phenomena during compression tests. The material constants of semisolid material in the stress-strain curve are proposed to perform the numerical analysis for a die design of semisolid forging. The starting materials used in this experiment are A357, 86S (similar to A319), and A390 alloys, which are fabricated by the electromagnetic stirring process. The intelligent compression test with a controlled strain rate was performed. The liquid segregation in the overall cross-sectional areas is controlled as the multistage variation of the pressing velocity and variation of the solid fraction during the compression process. The characteristics of materials flow between solid and liquid phases, considering the liquid segregation, are discussed for various solid fractions and pressing velocities.     

余热淬火循环泵数量对锻造转向节内部组织的影响

针对汽车转向节余热淬火容易出现淬火裂纹等质量问题,以江淮瑞风汽车转向节的余热淬火试验为例,通过启动一台和启动两台淬火介质循环搅拌泵,检测转向节在不同工况下的硬度剖面梯度、金相组织、晶粒度等级参数,并分别对其进行现场试验研究。通过分析热淬火油槽内循环搅拌泵的开启数量对转向节内部组织的影响,可知在温度和介质冷却特性不变时,循环搅拌泵开启台数对淬透层深度有明显的影响。并证明了开启两台循环搅拌泵是最佳选择,同时使用两台循环搅拌泵,既能保证冷却均匀性,又能提高锻件整体淬火硬度,还能提高金相组织级别。     

Tuning local structures in metallic glasses by cooling rate

The Zr₄₈Cu₄₅Al₇ amorphous alloy samples quenched under cooling rates of about 2 × 10⁶ K/s and 1 × 10² K/s were prepared by melt spinning and copper-mold suction casting, respectively. Synchrotron-radiation based experiments, combined with a series of calculations, were performed to study the microstructures in both samples. It was found that although the short-range orderings are similar in Zr-centered clusters for both samples, the atom arrangements and distributions in Cu- and Al-centered clusters are very different in terms of atomic-packing efficiencies and regularity of clusters in these two samples. A quantitative analysis revealed that the lower cooling rate leads to the higher packing efficiency and the higher regularity of clusters. This revealed how the cooling rate during quenching fine-tunes the atomic- and cluster-level microstructures in amorphous alloys with the same composition, which may be the structural basis to address the issue why macroscopic properties change with the cooling rate.     

真空高压混合气淬技术的发展

在真空热处理中,液体淬火正在被气淬所取代。提高淬火剂的热传递系数能提高厚壁件的冷却速率,用混合气体代替单一气体淬火可达到这一目的。举例介绍了国外应用混合气体提高气淬能力的研究情况。     

Coefficient of β-stabilization of titanium alloys

The coefficient of β-stabilizationK _β was introduced in Russia for titanium alloys in the seventies. It makes it possible to determine the class of the alloy from its chemical composition and evaluate approximately the mechanical properties. The present paper concerns the effect of various elements and the cooling rate in quenching onK _β. The limits of application of the coefficient of β-stabilization are determined. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 2–5, December, 1997.     

Characterisation of rosette formation in an aluminium–silicon alloy

Differential thermal analysis has been used to investigate the effect of cooling rate on rosette formation during solidification of a synthetic Al–Fe–Si alloy. Rosettes can be characterised as a very fine multiphase structure within more or less convex areas dispersed in the matrix. Their formation during solidification is related with liquid entrapment and high solidification undercooling associated with the need of independent nucleation events of second phases. It is here shown that their density and internal coarseness depend on cooling rate. Further, metallographic observation of rosettes in contact with large precipitate of β-Al₉Fe₂Si₂ phase allowed to conclude that this latter phase does not help silicon nucleation.     

液态淬火介质的两个共性的缺点及对策

适用范围有限和工件淬火变形大是液态淬火剂的两个带有共性的缺点,提出了克服第一个缺点即扩大液态淬火剂的应用范围的8种技术措施,指出,工件的淬火变形量除淬火介质的冷却速度外,还与其特性温度有关,应选用特性温度稳定的介质淬火。