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The present paper reports the investigation of the microstructure distribution of squeeze cast AZ91D alloy. The microstructure of squeeze cast AZ91D alloy is not uniform and is composed of four zones, which are chilled layer, segregation zone, pressured crystallisation area and hot spot area respectively. Moreover, in the pressured crystallisation area, the microstructure sequence in the transverse section from the outside to the inside could be divided into four sublayers, such as fine equiaxial dendrite area, dendrite area with a high directivity, confusion dendrite area and disorder dendrite area. The volume fraction of the intermetallic compound Mg17Al12 also varied with the location. The volume fraction of Mg17Al12 in the pressured crystallisation area is the largest except in the segregated zone. [ABSTRACT FROM AUTHOR]

The microstructures and tensile properties of boronized N80 steel pipes by pack boriding under four different cooling conditions were investigated. The boride layer was composed of FeB and Fe2B phases with a hardness range of 1200-1600 HV. Fan cooling and fan cooling with a graphite bar in the center of the boriding agent were employed to improve the tensile properties. As cooling velocity was increased, the thickness of boride layer and grain size of the steel substrate were consequently reduced, whereas the pearlite volume in steel substrate was increased, resulting in improvement of tensile properties. Boronized N80 steel pipe which was fan cooled with a graphite bar inside possessed the highest ultimate tensile strength and yield strength, in accordance with the mechanical properties required by API SPEC 5L. Fracture surface analysis revealed that the boronized N80 steel showed ductile fracture at room temperature. [ABSTRACT FROM AUTHOR]

The impact of heavy metal contamination on settling behavior and microstructure of kaolin-bentonite blends is evaluated via a series of sedimentation tests. The bentonite content in the blends varies from 0% (i.e., pure kaolin) to 15% by dry weight. Concentrated lead nitrate (Pb(NO 3 ) 2 ) solution with target lead (Pb) concentrations ranging from 0 (i.e., distilled deionized water) to 60 mmol/L is used as a representative heavy metal contamination. The blend subjected to the sedimentation test is prepared by both the conventional method (Method 1) and a new method (Method 2), in which Method 2 allows for sufficient chemical interaction between clay particles and concentrated Pb(NO 3 ) 2 solution. The results demonstrate that the sample preparation method, bentonite content, and Pb concentration considerably affects the settling behavior. A threshold Pb concentration (approximately 0.7 mmol/L to 2 mmol/L) is found to differentiate the settling behavior of the blends. The blend displays an accumulation sedimentation when the Pb concentration is lower than the threshold, otherwise it shows a flocculation/aggregation sedimentation. The final sediment volume ( SV F ), obtained at the termination of the sedimentation test (80 days), increases with increasing bentonite content. In addition, SV F increases with increasing Pb concentration when the blend shows the accumulation sedimentation; whereas opposite tendency of the SV F - Pb concentration relationship is found in the flocculation/aggregation sedimentation. A power function is derived for assessing the relationship between SV F and liquid limit of the blends tested in this study and soils reported in previous studies. In addition, the chemical compatibility, in terms of hydraulic conductivity and compression index, can be preliminarily assessed through combination of sediment volume ratio and liquid limit ratio. Finally, the micro-mechanisms controlling the change in settling behavior with lead concentration is addressed by analyzing microstructures of the sediments accumulated at the termination of sedimentation tests via scanning electron microscopy. [ABSTRACT FROM AUTHOR]