Tuning ductility for refractory high-entropy alloys

Development of new high-temperature materials, incorporating alloys based on metals with higher operating temperatures and melting points along with optimum properties, has always been motivated for their applications, typically in aerospace and marine industries. High-Entropy alloys (HEAs), or multicomponent alloys with equiatomic or close-to-equiatomic compositions, based on group IV, V and VI refractory elements, can be potential candidates due to their attractive high-temperature properties. However, inadequate ductility puts a limit on their mechanical performance for structural applications. A strategy is proposed here to design refractory HEAs with yield strength reaching 1000 MPa, and importantly with sufficient ductility at room temperature. Ductility is introduced by maintaining the number of total valence electrons low, and this is controlled by adjusting the alloy compositions. In addition, thermomechanical treatment is also utilized to further fine tune the mechanical properties via modifying the microstructure. Our findings will shed light on the design of refractory HEAs with optimal mechanical properties

A study of the effects of kaolin, solid filler on the processing, mechanical, and dynamic properties of some industrial rubbers cured with novel sulphur cure system

Two novel methods for the sulphur vulcanisation of NR, BR and EPDM rubbers using N-tert-butyl-2-benzothiazole sulphenamide (TBBS) accelerator and zinc oxide (ZnO) activator have been developed. In one method, the optimum loading of TBBS and ZnO were measured for some sulphur-filled NR, BR and EPDM rubbers. The cure systems for the NR were (S/TBBS/ZnO), (1/1.5/0.2), (2/1.5/0.3), (3/1.5/0.25), and (4/3.5/0.2), for the BR, (0.5/1.75/0.2) and (1/3/0.2), and for the EPDM, (1/1/0.075). The cure was very efficient in spite of reducing the amount of TBBS and ZnO chemicals. In another method which used a single additive component in the form of a powder (TBBS/ZnO: 350mg/1g), the loading of the powder in NR was raised increasingly from 0.63 to 5.63 phr, the scorch time was unchanged and the optimum cure time reduced at 1.25 phr powder. The rate of cure accelerated at 1.25 phr powder. The crosslink density reached its maximum value at 5.63 phr powder. This method reduced the TBBS and ZnO requirement in the cure system by 85wt%. Solid kaolin filler pre-treated with a sulphur-bearing mercaptosilane was used to reinforce NR, BR and EPDM rubbers. For NR, to react the sulphur in the silane on the kaolin surface with the rubber chains and optimise the reaction between the two, 16 phr TBBS and 0.2 phr ZnO were added to the kaolin-filled rubber. The hardness and Young s modulus increased and compression set decreased when up to 3 phr elemental sulphur was included in the kaolin-filled rubber with 16 phr TBBS and 0.2 phr ZnO. The tensile strength, elongation at break, stored energy density at break, and tear energy of the rubber vulcanisate reduced when elemental sulphur was added. Notably, the inclusion of elemental sulphur was the key factor in controlling the rubber properties. In an extended work, 60 phr silane pre-treated kaolin was mixed with NR, BR and EPDM and the rubbers were cured using the novel cure systems developed earlier. The effect of 140 phr kaolin on the properties of NR was also investigated. For NR, the hardness increased by 64% when 60 phr kaolin was added and the trend continued rising by another 28% when the loading of kaolin reached 140 phr. Similarly, the Young s modulus rose by 170% with 60 phr kaolin and then by an extra 148% when the full amount of kaolin, i.e. 140 phr, was reached. The tensile strength and tear energy were unchanged and the elongation at break and stored energy density at break deteriorated by a total of 65% and 34%, respectively with 140 phr kaolin. The compression set of the unfilled rubber was 41%, and it then rose to 64% and 71%, when 60 and 140 phr kaolin was added, respectively. For BR, the hardness increased by 23% and for EPDM, by 34%, respectively when 60 phr kaolin was incorporated in the rubbers. For BR, the tensile strength, elongation at break and Young s modulus rose by 759%, 256% and 114%, respectively. The compression set of the unfilled BR was 9.4%, and subsequently rose to 26% when 60 phr kaolin was mixed with the rubber. For EPDM, the tensile strength, elongation at break and Young s modulus improved by 964%, 332% and 71%, respectively. For BR, the stored energy density at break and tear energy were increased by 2442% and 536%, respectively and for EPDM, by 3133% and 1479%, respectively. The compression set of the unfilled EPDM was 39%, and afterward increased to 48% with 60 phr kaolin. Kaolin was found to be extending or non-reinforcing filler for the strain-induced crystallising NR and highly reinforcing for the non-crystallising BR and EPDM

Predicting the solid solubility limit in high-entropy alloys using the molecular orbital approach

© 2015 AIP Publishing LLC. High-entropy alloys (HEAs) are currently at the research frontier of metallic materials. Understanding the solid solubility limit in HEAs, such a highly concentrated multicomponent alloy system, is scientifically intriguing. It is also technically important to achieve desirable mechanical properties by controlling the formation of topologically or geometrically closed packed phases. Previous approaches to describe the solid solubilities in HEAs could not accurately locate the solubility limit and have to utilize at least two parameters. Here, we propose to use a single parameter, the average energy of d-orbital levels, Md, to predict the solid solubility limit in HEAs. It is found that Md can satisfactorily describe the solid solubilities in fcc structured HEAs containing 3 d transition metals, and also in bcc structured HEAs. This finding will greatly simplify the alloys design and lends more flexibility to control the mechanical properties of HEAs. When 4 d transition metals are alloyed, Md alone cannot describe the solid solubility limit in fcc structured HEAs, due to the large increase of the bond strength that can be gauged by the bond order, Bo. The potential opportunities and challenges with applying the molecular orbital approach to HEAs are discussed

Kaolin reinforcement of some rubbers with novel sulfur cure systems

A large amount of kaolin (China clay) was used to reinforce the hardness, tensile strength, elongation at break, stored energy density at break, tear resistance, and Young’s modulus of some sulfur-cured NR, BR and EPDM. The kaolin surface had been pre-treated with 3-mercaptopropyltrimethoxysilane (MPTS) to reduce its polarity and prevent it from adsorbing moisture which could have been detrimental to the cure of the rubbers. For NR, the hardness and Young’s modulus improved, tensile strength and tear resistance were unchanged and the remaining properties deteriorated when kaolin was added. The viscosity increased and the scorch and optimum cure times decreased with kaolin. The highest cure rate ever reported for a sulfur-cured NR-based compound was achieved when kaolin was mixed with the rubber. For BR and EPDM, most of the properties including the viscosity gained significantly from the presence of kaolin in the rubbers. It was concluded that kaolin was an extending or non-reinforcing filler for NR, and highly reinforcing for BR and EPDM. Notably, the scorch and optimum cure times and cure rate of BR benefited so much, whereas with the exception of the scorch time, the optimum cure time and cure rate of EPDM were adversely affected by kaolin. The addition of kaolin increased the crosslink density of NR but had a detrimental effect on the crosslink density of BR and EPDM. The early indications are that kaolin is a viable alternative to carbon black and silica/silane systems in rubber reinforcement

Analysis of Case Records of Foetal Deaths in Livestock in Serdang, Selangor

Cases of foetal death in the necropsy records of the Faculty of Veterinary Medicine and Animal Science, Universiti Pertanian Malaysia over a 5-year period (1977 -1981) were analysed. Of 119 foetal deaths, 49.0% were abortions, 41.0% stillbirths and 10.0% premature non-viable births. Most of the cases, particularly abortions, (96.5%) remained undiagnosed. There was a remarkable absence of foetal deaths due to infectious diseases

Major reduction in chemical curatives for rubber articles

The sulfur cure system in the ethylene-propylene-diene (EPDM)-based Curtain Wall Seal (CWS) has two accelerators, adding up to 2.75 parts per hundred rubber (phr) by weight, and two activators (ZnO: 5phr, stearic acid:1phr). In total, 8.75phr chemicals are used to fully cure the article with 1phr elemental sulfur. Excessive use of chemical curatives is harmful to health, safety, and the environment. A new method uses experimental results from high temperature cure tests to provide highly efficient cure systems for industrial rubber articles, which requires a lot less chemical curatives without compromising cure efficiency. This method can be applied to reduce chemical curatives in other industrial rubber articles

Alloy Design for High-Entropy Alloys: Predicting Solid Solubility, and Balancing Mechanical Properties and Oxidation Resistance

High-entropy alloys (HEAs) comprise of multi-principal elements in equi-atomic or near equi-atomic percentage. HEAs are considered as potential structural materials for high temperature applications, which require alloy design for optimum mechanical properties. In this regard, achieving both high strength and tensile ductility is still a great challenge. Compared to conventional alloys, HEAs have high configurational entropy, which tends to stabilize the solid solution formation, mainly face-centered-cubic (fcc) and/or body-centered-cubic (bcc) solid solutions. Generally, fcc-type HEAs are ductile but soft, while bcc-type HEAs are hard but brittle. \ua0\ua0This project has three working directions. The first part of this work is related to alloy design and aims to gain improved understanding of the solid solubility in HEAs. The difficulties that are encountered by HEAs are mostly related to the alloy design strategy. Previous approaches to describe the solid solubilities in HEAs could not accurately locate the solubility limit. Therefore, the need for single-phase solid solution and controlling the formation of secondary phases is addressed through the molecular orbital approach. The output of this approach is the introduction of the Md parameter, the d-orbital energy level to HEAs, which can well describe the solubility limit in HEAs. To further develop this approach, Md is also complemented with theoretical methods specifically, CALPHAD and experimental work.\ua0The second part of this work is to ductilize HEAs containing group IV (Ti, Zr, Hf), V (V, Nb, Ta) and VI (Cr, Mo, W) refractory elements, known as refractory HEAs (RHEAs), where inadequate ductility puts a limit on their mechanical performance for structural applications. A strategy is proposed to design RHEAs with sufficient yield strength combined with ductility at room temperature. Ductility is introduced by maintaining the bcc single-phase solid solution and keeping the number of total valence electrons low, which can be achieved through controlled alloying. More importantly, a mechanism and route for ductilizing RHEAs is proposed. \ua0The third part, which is the ultimate goal of this work, is to address the balance of mechanical properties and oxidation resistance for RHEAs, for the optimal development of RHEAs aiming at high-temperature applications. Based on the known facts for refractory alloys, the oxidation resistance is also problematic for RHEAs and there exists only limited work towards the study of high temperature oxidation of ductile RHEAs. Therefore, the oxidation mechanism is studied and it is found out that the insufficient oxidation resistance in existing ductile RHEAs is attributed to the failure in forming protective oxide scales accompanied by the accelerated internal oxidation leading to pest-disintegration or pesting. Efforts are also carried out to improve oxidation resistance via alloying and pack-cementation aluminizing. These studies provide important input to the further development of RHEAs as novel high-temperature materials and shed light on the design of refractory HEAs with optimal mechanical and oxidation resistance properties

Development of Innovative Load Transfer Mechanism to Reduce Hurricane-Induced Failures in New and Existing Residential Construction

Implicit in current design practice of minimum uplift capacity, is the assumption that the connection\u27s capacity is proportional to the number of fasteners per connection joint. This assumption may overestimate the capacity of joints by a factor of two or more and maybe the cause of connection failures in extreme wind events. The current research serves to modify the current practice by proposing a realistic relationship between the number of fasteners and the capacity of the joint. The research is also aimed at further development of non-intrusive continuous load path (CLP) connection system using Glass Fiber Reinforced Polymer (GFRP) and epoxy. Suitable designs were developed for stud to top plate and gable end connections and tests were performed to evaluate the ultimate load, creep and fatigue behavior. The objective was to determine the performance of the connections under simulated sustained hurricane conditions. The performance of the new connections was satisfactory