Preparation of AlCoCrFeNiTi0.5 high entropy alloy by SPS from mechanically alloyed powders

High entropy alloys are newly developed class of materials with excellent properties and promising application potential. The present work reports synthesis of inequiatomic alloy AlCoCrFeNiTi0.5 prepared by mechanical alloying (MA) in planetary ball mill followed by spark plasma sintering (SPS). Alloying behaviour, microstructure, basic mechanical properties and thermal behaviour of the alloy were investigated by means of XRD, SEM and DSC analyses and microhardness testing. It was found that the MA process parameters significantly influence homogeneity and size of the obtained alloyed powders. During MA, Cr-based supersaturated solid solution with body-centered cubic (BCC) structure was formed. After SPS at 1000\ub0C the fine grained microstructure consisted of BCC solid solution and ordered FCC phase. Low levels of retained porosity were observed. The alloy exhibited a high hardness of 762HV

Effect of heat treatment on microstructure and mechanical properties of spark plasma sintered AlCoCrFeNiTi0.5 high entropy alloy

The present work is focused on synthesis and heat treatment on non-equiatomic AlCoCrFeNiTi0.5 high entropy alloy (HEA) with a composite structure reinforced by TiC nanoparticles. The initial alloy was prepared by mechanical alloying (MA) in a planetary ball mill, compacted by spark plasma sintering (SPS) and heat treated at different temperatures. Mechano-chemical reactions during the MA process as well as the microstructure and hardness of the SPS-ed compacts prior to and after the heat treatment were investigated. During MA, Cr-based supersaturated solid solution with the BCC structure was formed. After SPS at 1100 \ub0C, the BCC solid solution decomposed into nano-grained microstructure consisting of FCC and ordered BCC solid solutions, σ phase, and in-situ formed TiC nanoparticles. The high hardness of the alloy (762 HV) was retained after the subsequent heat treatment at 1100 \ub0C (603 HV). It was shown that the fabrication of TiC reinforced nanocomposites from elemental powders without the use of expensive nanograined powders can be achieved

Assessment and Protection Plan for the Nawiliwili Watershed: Phase 1-Validation and Documentation of Existing Environmental Data

This report documents the findings for Phase 1 of a three-phase study that is aimed at assessing the status of the Nawiliwili Watershed on Kaua’i and developing a plan for its future protection. The objectives of this phase include utilizing sources of existing information to assess current land use in the area and identifying sources and levels of pollutants believed to be present in the watershed based on past studies relevant to the project area. Sources of information included available documents, persons who are familiar with the area, and questionnaires mailed to concerned individuals. Letters mailed to landowners and operators in the watershed area asked for their input. Information was also obtained at community meetings. The study also benefited from a local advisory committee that included government individuals and environmental groups. Data concurrently collected by the Nawiliwili Bay Watershed Council are also used here. The study concluded that little hard scientific data exist for the Nawiliwili Watershed, especially baseline data. The Hawai’i Department of Health’s current Total Maximum Daily Load (TDML) studies may provide public information that could be useful in assessing the health of the watershed. Since more baseline data are being made available, there is a chance to systematically define changes and trends in the watershed. The study identified sediment, nutrient, and bacterial-contamination problems in the Nawiliwili watershed and bay. Sediment sources include agricultural lands, construction sites, channel alteration, stream erosion, a quarry, and urban runoff. Nutrients originate from agriculture practices, golf courses, cesspools, frosted areas, urban runoff, and wastewater treatment spills. Bacterial contamination originates from cesspools, frosted areas, urban runoff, and wastewater treatment spills. There is, however, a chance that chemicals from other sources are also present. The absence of data has created great uncertainties regarding quantification and assessment of such contaminants. Only the levels of bacterial contamination are defined based on available measurements. Additional studies are needed to assess the existence of other chemicals in the watershed and their respective concentration. There is also a need to assess the various sources of bacterial contamination to define the level of contaminant caused by each. A fairly extensive list of potential sources of pollution has been identified which can provide a base for choosing sites for data collection and for sampling-scheme design. There is a need for new data to confirm these findings. The study used the state of Hawai’i’s web site on the Internet to identify relevant geographic information system maps of the area. There is a need, however, to update land-use information, which has changed in recent years. Finally, there is a need to increase or improve on the availability of public and private information about the watershed and to maintain strong ties and full cooperation between environmental groups and landowners/operators. With availability of information and full cooperation of all parties involved, a better understanding of the various processes will be gained. Developing sound approaches to remediate and protect the watershed is a goal that should be easy to reach. Scientific research can provide methods and approaches to maximize economic benefits from the watershed without negatively affecting the environmental quality.State of Hawai'i, Department of Health, Clean Water Branch: ASO Log No. 02-10