Epoxidized Soybean Oil: Evaluation of Oxidative Stabilization and Metal Quenching/Heat Transfer Performance

Vegetable and animal oils as a class of fluids have been used for hundreds of years, if not longer, as quenchants for hardening steel. However, when petroleum oils became available in the late 1800s and early 1900s, the use of these fluids as quenchants, in addition to their use in other industrial oil applications, quickly diminished. This was primarily, but not exclusively, due to their generally very poor thermal-oxidative instability and the difficulty for formulating fluid analogs with varying viscosity properties. Interest in the use of renewable fluids, such as vegetable oils, has increased dramatically in recent years as alternatives to the use of relatively non-biodegradable and toxic petroleum oils. However, the relatively poor thermal-oxidative stability has continued to be a significant reason for their general non-acceptance in the marketplace. Soybean oil (SO) is one of the most highly produced vegetable oils in Brazil. Currently, there are commercially produced epoxidized versions of SO which are available. The objective of this paper is to discuss the potential use of epoxidized SO and its heat transfer properties as a viable alternative to petroleum oils for hardening steel.     

Heat Transfer Properties of a Series of Oxidized and Unoxidized Vegetable Oils in Comparison with Petroleum Oil-Based Quenchants

Vegetable oils, especially soybean oil, exhibit substantially poorer thermal-oxidative stability than commercially available petroleum oil quenchant formulations. Therefore, to achieve any commercially interesting performance, vegetable oils must be stabilized by the addition of antioxidant inhibitors. This work describes the ability of two commercially available antioxidants, Irganox L 57 and Irganox L 109, to stabilize soybean oil against thermal-oxidative degradation. In addition, the effect of antioxidant stabilization on quenching performance was evaluated by determining the profile of heat transfer coefficient variation throughout the quenching process at different times after being subjected to an accelerated thermal-oxidation aging test. The results of this work are discussed here.     

植物油的氧化及其对淬火特性的影响

传统上,矿物油是常用淬火剂中最重要的一类淬火剂。然而,它们在本质上缺乏环保性,又有毒性,再从长期低价供应角度考虑,有必要寻找新的替代介质。石油制品油的淬火特性与其成分很有关系,因而受其氧化降解性能的限制。由于不断暴露在钢与油接触面问相对较高的温度中,石油制品油遭受热降解和氧化降解,使得其淬火特性发生明显变化。因此,淬火特性是任何一种可选择的淬火介质都必须要检验的一个非常重要的性能参数。可供选择的一类液态物质为植物油,它们具有典型的生物降解特性并且无毒。然而,植物油具有相对较差的抗氧化稳定性能,因此测定氧化对其淬火特性的潜在影响具有重要意义。本文报导的结果仅是这项巨大研究中的第一步,在这项工作中,对不受禁止的植物油的试验是在实验室设备上进行的,以前报告的促使石油制品油早期氧化的过程接近实际使用条件。依照ASTM D 6200标准,使用粘度计、红外线分光镜、^13CMR分光镜以及冷却曲线特性测定方法对所研究的液态植物油进行了性能检测并和典型的石油制品油作了成分比较。所得的结果表明,作为淬火介质,植物油是有前景的石油制品油的替代品,但在商业上要可行,同时必须使用适当的抗氧化剂。     

防老化剂对大豆油和棕榈油基淬火剂耐氧化性和淬火冷却性能的影响(英文)

尽管以往已有过关于多种植物油的淬火冷却性能的报道,但有关防老化剂对这些油的耐氧化性和初期淬火冷却性能的影响的报道却不多见。本文评估了两种饱和度有很大差异的常用油即大豆油和棕榈油,其相对耐氧化性对淬火冷却性能的影响,并测定了常用的市场有售的常用防老化剂对这些油的防老化效果。除了测定相对耐氧化性外,还通过冷却曲线分析进一步评述了防老化剂对大豆油和棕榈油的初期淬火冷却性能的影响。     

Stability in Phase Transformation After Multiple Steps of Marforming in Ti-Rich Ni-Ti Shape Memory Alloy

Nickel-titanium (Ni-Ti) alloys are the most attractive among shape memory alloys (SMA) due to their good functionality properties coupled with high strength and ductility. The transformation temperatures in Ti-rich Ni-Ti SMA can be altered by subjecting them to suitable thermal and/or mechanical treatments to obtain martensitic transformation in one or more steps above 0 °C. The goal of the present work is to investigate the stability of phase transformation characteristics, such as, type of sequence (one, two, and multiple steps) and transformation temperatures in Ti-Rich Ni-Ti SMA (Ni-51 at.%Ti), after being subjected to an initial heat treatment at 500 °C for 30 min in air followed by multiple steps of marforming (cold rolling, 30% thickness reduction) intercalated with heat treatments at 500 °C for 30 min in air and a final heat treatment at four different temperatures (400, 450, 500, and 600 °C) for 30 min in air atmosphere. Differential scanning calorimetry (DSC) and electrical resistivity (ER) were used to identify the phase transformation sequences and the stability of transformation temperatures during initial 10 thermal cycles for each sample with distinct thermo-mechanical treatment.     

Plasma Spraying of Silica-Rich Calcined Clay Shale

Silica-rich clay shale is a viable candidate for replacement of mullite in many applications, especially when outstanding refractoriness and chemical resistance to various agents are desirable. In this contribution, instead of the commonly used synthetic mullite feedstock, the thermal stability of inexpensive calcined natural raw clay shale sprayed using water stabilized plasma system is reviewed. Phase stability and phase changes at elevated temperatures up to 1500 °C were studied by an array of experimental techniques ranging from measurements of thermal conductivity and the heat flow as functions of temperature, scanning electron microscopy, x-ray diffraction (XRD) of the annealed samples, and in situ high temperature XRD. The mostly amorphous as-sprayed coatings with less than 10 wt.% of mullite are temperature stable up to 800 °C and rapid crystallization occurs between 920 and 940 °C. Performed analyses gave evidence about the increase of mullite grain sizes for temperatures higher than 1200 °C and, moreover, certain saturation of crystallinity, not surpassing the threshold of 60 wt.% even for 1500 °C, is observed. The microstructure after annealing at 1500 °C is notable by clusters of fine needle-like mullite crystallites with sizes within the range of tens of nanometers in Si-rich amorphous matrix.     

Low Solution Temperature Heat Treatment of AlSi<Subscript>9</Subscript>Cu<Subscript>3</Subscript>(Fe) High-Pressure Die-Casting Actual Automotive Components

Usually, high-pressure die-casting (HPDC) components cannot be heat-treated at high temperature without the occurrence of surface blisters, which are unacceptable for surface finish and may reduce the mechanical properties. In this context, the purpose of the present paper was to analyze the effectiveness of special low solution temperature T6 heat treatment in overcoming this limit for HPDC AlSi₉Cu₃ alloy. Very low solution temperatures (<?450 °C, followed by 165 °C aging) to prevent the occurrence of blisters were combined with commonly used times (from 1 to 16 h) ensuring the feasibility of industrial application. Treatments were conducted on samples extracted from actual castings to evaluate the typical defects encountered in common production. Properties were analyzed by means of visual inspection, microstructural observations, image analysis, hardness, tensile tests and fractography. The results showed that it is possible to use solubilization temperatures below 450 °C for several hours in a T6 treatment to give strengthening without relevant blistering in AlSi₉Cu₃ alloy. The optimum match of properties was provided by a solution treatment at 430 °C for 4 h followed by an aging at 165 °C for 8 h, which gave a yield increase of ~?50 MPa, an increase in ductility and the best Quality Index value.     

Friction and Wear Behavior of 30CrMnSiA Steel at Elevated Temperatures

The friction and wear properties of 30CrMnSiA steel were investigated at elevated temperature from 100 to 600 °C. Thereafter, the wear debris and worn surfaces were examined to understand the wear mechanisms. The remained debris with relatively high hardness created three-body abrasion at lower temperatures (100-300 °C). Abrasive wear prevailed at the conditions with high friction coefficients and wear rates. A significant change in friction and wear behavior occurred at 400 °C. At the temperature of 400 °C, oxidation induced mild wear was found because of the formation of load-bearing oxide film. Both the friction coefficients and wear rates of the steel were lowest at 400 °C. At the temperatures of 500-600 °C, a mild-to-severe wear transition occurred which resulted in an increase in the friction coefficients and wear rates of the steel. This is related to the decrease in the strength of matrix and hardness of worn surfaces and subsurfaces. The predominant wear mechanism is considered to be severe abrasive, adhesive wear and a fatigue delamination of the oxide film.     

Oxidation Behaviour of Model Cobalt-Rhenium Alloys During Short-Term Exposure to Laboratory Air at Elevated Temperature

The alloys being used in high-temperature systems such as stationary gas turbines and aircraft engines are iron-, cobalt- and nickel-based superalloys, amongst which the latter is the most widely used for highest temperatures. However, the use of Ni-based alloys is limited to temperatures below 1,100 °C. The experimental Co–Re-based alloys are promising for high-temperature applications for service temperatures beyond 1,200 °C. The purpose of the present investigations, at this still early stage of the alloy development, is to gain a first insight into the oxidation mechanisms and to find ways to improve oxidation resistance of this class of materials. Thermogravimetric studies in combination with microstructural examinations of six model Co–Re alloys with different compositions showed the negative influence of rhenium on the oxidation resistance of Co-based alloys due to evaporation of rhenium oxide(s). Oxidation at 1,000 °C in air yielded an oxide scale, that consists of a Co-oxide outer layer on a thick and porous Co–Cr oxide and a semicontinuous and therefore non-protective Cr-oxide film on the base metal substrate. This allowed for the vaporization of rhenium oxide formed during oxidation and hence led to a loss of Re. Computer-aided thermodynamic calculations were carried out to supplement the experimental analyses and were found to reasonably predict the stability ranges of the various oxide phases observed.     

Forming-Limit Diagrams for Magnesium AZ31B and ZEK100 Alloy Sheets at Elevated Temperatures

Modern design and manufacturing methodologies for magnesium (Mg) sheet panels require formability data for use in computer-aided design and computer-aided engineering tools. To meet this need, forming-limit diagrams (FLDs) for AZ31B and ZEK100 wrought Mg alloy sheets were developed at elevated temperatures for strain rates of 10^?3 and 10^?2 s^?1. The elevated temperatures investigated range from 250 to 450 °C for AZ31B and 300 to 450 °C for ZEK100. The FLDs were generated using data from uniaxial tension, biaxial bulge, and plane-strain bulge tests, all carried out until specimen rupture. The unique aspect of this study is that data from materials with consistent processing histories were produced using consistent testing techniques across all test conditions. The ZEK100 alloy reaches greater major true strains at rupture, by up to 60%, than the AZ31B alloy for all strain paths at all temperatures and strain rates examined. Formability limits decrease only slightly with a decrease in temperature, less than 30% decrease for AZ31B and less than 35% decrease for ZEK100 as the temperature decreases from 450 to 300 °C. This suggests that forming processes at 250-300 °C are potentially viable for manufacturing complex Mg components.     

Properties and Heat Treatment of High Transition Temperature Ni-Ti-Hf Alloys

The high transition temperature Ni-Ti (Hf, Zr) alloys have long been of interest for actuators and other applications requiring transition temperatures greater than 100 °C. Unfortunately, the high hardness and poor fabricability of these alloys have prohibited the scale up to commercial production. Some of these alloys are so “hot short” that even modest size ingots cannot be cast without internal cracks formed by solidification shrinkage stresses. Hot rolling methods have recently been demonstrated that can produce crack free Ni-Ti-(6-10 at.%)Hf thin sheets having austenite transition temperatures up to approximately 170 °C. Since these alloys are soft martensite phase at room temperature, they can easily be formed and bent at ambient temperature but cold rolling can only be performed to a limited extent due to high work hardening rates which are typical for Ni-Ti alloys. Progress is now underway to scale up these methods to produce 500-600 mm wide sheets. The effects of composition variations, heat treatment and cold working on transition temperatures are discussed. Microstructural features unique to these ternary alloys and impurity effects are also discussed. The effects of stress on transition temperature have been determined. Austenite transition temperatures, as measured by DSC and bend-free recovery testing, can be controlled within 100-170 °C for these alloys.     

Higher Temperature Thermal Barrier Coatings with the Combined Use of Yttrium Aluminum Garnet and the Solution Precursor Plasma Spray Process

Gas-turbine engines are widely used in transportation, energy and defense industries. The increasing demand for more efficient gas turbines requires higher turbine operating temperatures. For more than 40 years, yttria-stabilized zirconia (YSZ) has been the dominant thermal barrier coating (TBC) due to its outstanding material properties. However, the practical use of YSZ-based TBCs is limited to approximately 1200 °C. Developing new, higher temperature TBCs has proven challenging to satisfy the multiple property requirements of a durable TBC. In this study, an advanced TBC has been developed by using the solution precursor plasma spray (SPPS) process that generates unique engineered microstructures with the higher temperature yttrium aluminum garnet (YAG) to produce a TBC that can meet and exceed the major performance standards of state-of-the-art air plasma sprayed YSZ, including: phase stability, sintering resistance, CMAS resistance, thermal cycle durability, thermal conductivity and erosion resistance. The temperature improvement for hot section gas turbine materials (superalloys & TBCs) has been at the rate of about 50 °C per decade over the last 50 years. In contrast, SPPS YAG TBCs offer the near-term potential of a > 200 °C improvement in temperature capability.     

Thermodynamic and Kinetics Aspects of High Temperature Oxidation on a 304L Stainless Steel

An AISI 304L stainless steel was oxidised in a TGA instrument at temperatures ranging from 800 to 1,200 °C and for up to 3 h. The measured weight gains were fitted starting from the Wagner model, taking into account both a linear and a parabolic behaviour. Rate constants and activation energies were calculated. The fraction of oxides as a function of annealing time at 1,050 °C were estimated by Rietveld refinement of XRD patterns of oxidised samples. These data were compared with the theoretical equilibrium conditions calculated with the Calphad approach. A simplified model able to describe the main kinetic features of the oxidation of an AISI 304L steel in industrial conditions (1,050 °C and 0.087 atm of oxygen partial pressure) was developed.     

Oxidation Behavior of Carbon Steel: Effect of Formation Temperature and pH of the Environment

The nature of surface oxide formed on carbon steel piping used in nuclear power plants affects flow-accelerated corrosion. In this investigation, carbon steel specimens were oxidized in an autoclave using demineralized water at various temperatures (150-300 °C) and at pH levels (neutral, 9.5). At low temperatures (< 240 °C), weight loss of specimens due to dissolution of iron in water occurred to a greater extent than weight gain due to oxide formation. With the increase in temperature, the extent of iron dissolution reduced and weight gain due to oxide formation increased. A similar trend was observed with the increase in pH as was observed with the increase in temperature. XRD and Raman spectroscopy confirmed the formation of magnetite. The oxide film formed by precipitation process was negligible at temperatures from 150 to 240 °C compared to that at higher temperatures (> 240 °C) as confirmed by scanning electron microscopy. Electrochemical impedance measurement followed by Mott–Schottky analysis indicated an increase in defect density with exposure duration at 150 °C at neutral pH but a low and stable defect density in alkaline environment. The defect density of the oxide formed at neutral pH at 150-300 °C was always higher than that formed in alkaline environment as reported in the literature.     

Processing of red ceramics incorporated with encapsulated petroleum waste

In petroleum extraction industry large amounts of oily sludge have to be discarded. This waste is usually considered of difficult final disposal, causing economical and environmental problems. This work reports on the re-use petroleum waste for manufacturing of red ceramic product used in civil construction. Ceramic pieces containing up to 30 wt.% of petroleum waste were uniaxially pressed and fired at temperatures ranging from 800 °C to 1000 °C. The technological properties (linear shrinkage, water absorption, apparent density, and compressive strength) as function of firing temperature and waste addition are presented. The results showed that the use of up to 30 wt.% of encapsulated petroleum waste into red ceramic pieces is technically adequate and cause less environmental impact.     

Hot Tensile Deformation Characteristics and Processing Map of Extruded AZ80 Mg Alloys

The hot deformation behaviors of extruded AZ80 Mg alloys were investigated using tension tests. True stress-true strain curves were obtained for deformation at temperatures from 250 to 450 °C with the strain rate range from 0.001 to 0.08 s^?1. Optical microscopy analysis was performed to correlate microstructural changes to the flow behaviors. Based on the flow stress, the processing map at a strain of 0.18 was developed using the dynamic materials model theory and can be divided into three zones, including stability zones, change-over region, and instability zones. In stability zones, there are two dynamic recrystallization regions: one region with a peak efficiency of 58% at 350 °C and a strain rate of 0.001 s^?1 called domain I; another region with a peak efficiency of 58% at 400 °C and a strain rate of 0.01 s^?1 taken as domain II. The apparent activation energy for domain I was estimated to be 100.71 kJ/mol, indicating that short-circuit diffusion process is along the grain boundaries and falls at lower temperatures and lower strain rates. A lattice self-diffusion is considered to be rate controlling mechanism with the apparent activation energy estimated as 140.32 kJ/mol at higher temperatures and higher strain rates in domain II. The change-over region is the zone from domain I to domain II, in which the grains abnormally grow. In instability zones, twins, local deformation band, wedge cracking, and matrix cracking were observed, suggesting that these processing parameters for hot tension in this zone are inapplicable.     

Synthesis,Fabrication and Characterization of ZnO-Based Thin Films Prepared by Sol–Gel Process and H<Subscript>2</Subscript> Gas Sensing Performance

In this paper, an attempt is made to deposit ZnO thin films using sol–gel process followed by dip-coating method on p-silicon (100) substrates for intended application as a hydrogen gas sensor owing to the low toxic nature and thermal stability of ZnO. The thin films are annealed under annealing temperatures of 350, 450 and 550 °C for 25 min. The crystalline quality of the fabricated thin films is then analyzed by field-emission scanning electron microscopy and transmission electron microscope. The gas sensing performance analysis of ZnO thin films is demonstrated at different annealing temperatures and hydrogen gas concentrations ranging from 100 to 3000 ppm. Results obtained show that the sensitivity is significantly improved as annealing temperature increases with maximum sensitivity being achieved at 550 °C annealing temperature and operating temperature of 150 °C. Hence, the modified ZnO thin films can be applicable as H₂ gas sensing device showing to the improved performance in comparison with unmodified thin-film sensor.     

The erosion‐corrosion resistance of uncoated and aluminized 12% chromium ferritic steels under fluidized‐bed conditions at elevated temperature

In this paper, some results from a study of the erosion‐corrosion resistance of uncoated and aluminized 12% chromium steel in a fluidized‐bed rig are reported. The aims of the research are to establish and compare the erosion‐corrosion resistance of these materials for possible applications as heat exchangers in future power plants, and to obtain an increased understanding on their behaviour and mutual superiority in a range of conditions. Damage to the uncoated 12% chromium steel occurs by an oxidation‐affected erosion process under all the studied conditions, with spallation of scale being the primary mechanism of material wastage. At a temperature of 550°C, the uncoated steel follows the typical angle‐dependence of a brittle material, while, at temperatures above 550°C, it follows an angle‐dependence that is more typical of a ductile material. This change in the angle‐dependence with temperature is related to characteristics, i.e. uniformity, adhesion and density, of the formed oxide scales. The rate of material wastage increases with increase in speed and temperature, due to the development of thicker, more uniform and more dense oxide scales, that promote more severe scale spallation. The erosion‐corrosion behaviour of the aluminized 12% chromium steel changes in the temperature range from 600°C to 650°C. This is due to a shift from a brittle‐like to a ductile‐like angle‐dependence and to a more rapid oxide scale build‐up at temperatures above 600°C. At an impact angle of 30° and at 550°C and 600°C, the prevailing erosion‐corrosion process for the aluminized steel is oxidation‐affected erosion. At 650°C and 700°C for an impact angle of 90°, the primary erosion‐corrosion mode is essentially erosion‐enhanced oxidation. The results of the study have also demonstrated that the Al₅Fe₂ coating deposited by pack aluminization offers enhanced protection against erosion‐corrosion at shallow impact angles at 550°C and 600°C and at steeper impact angles at 700°C.     

Functional Characterization of a Novel Shape Memory Alloy

A novel shape memory alloy (SMA) has been developed as an alternative to currently available alloys. This alloy, commercially known by its proprietary brand SMARQ, shows a higher working range of temperatures with respect to the SMA materials used until now in actuators, limited to environment temperatures below 90 °C. SMARQ is a high temperature SMA (HTSMA) based on a fully European material technology and production processes, which allows the manufacture of high quality products, with tuneable transformation temperatures up to 200 °C. Both, material and production processes have been evaluated for its use in space applications. A full characterization test campaign has been completed in order to obtain the material properties and check its suitability to be used as active material in space actuators. In order to perform the functional characterization of the material, it has been considered as the key element of a basic SMA actuator, consisting in the SMA wire and the mechanical and electrical interfaces. The functional tests presented in this work have been focused on the actuator behavior when heated by means of an electrical current. Alloy composition has been adjusted in order to match a transition temperature (As) of +145 °C, which satisfies the application requirements of operating temperatures in the range of ?70 and +125 °C. Details of the tests and results of the characterization test campaign, focused in the material unique properties for their use in actuators, will be presented in this work. Some application examples in the field of space mechanisms and actuators, currently under development, will be summarized as part of this work, demonstrating the technology suitability as active material for space actuators.