A. Albiter

Microstructure and heat-treatment response of Al-2024/TiC composites

Abstract Composites of a commercial Al-2024 alloy reinforced with particulate TiC have been produced by the pressureless melt infiltration route. Infiltration was carried out at 1200°C for 2 h and composite materials containing 52 and 55 vol.% TiC were obtained. The phases other than the matrix and the reinforcement were identified as CuAl2, AlTi3, Ti3AlC, and TiAl3. It was found that the composites were age hardenable after solutionizing at 530°C for 150 min and subsequent natural or artificial ageing at 190°C. Mechanical properties of the composites, as-fabricated and heat-treated, showed a strong dependency on the ceramic content. After heat treatment, the 55% TiC composites showed an increase of hardness from 28.5 to 38.5 HRC; meanwhile ultimate tensile strength increased from 379 to 480 MPa. A similar behavior, as a function of heat treatment, was observed for the composites containing 52% TiC, but the estimated values were lower than those obtained for the 55% TiC composites. Scanning electron microscope (SEM) examination revealed transgranular fracture throughout the CuAl2 agglomerated precipitates in the as-fabricated composites. In the heat-treated conditions, brittle and intergranular fractures were observed.

Structural and mechanical properties of the AlFe intermetallic alloy with Li, Ce and Ni additions

Microstructural and mechanical properties of AlFe intermetallic alloys with additions of Li, Ni, Ce and combinations of (Ce, Ni) and (Ce, Li) were obtained. The alloys were produced with normal casting techniques using SiC crucibles. Compression tests were carried out and some insights on the alloys mechanical properties are withdrawn. The main effect of these elements on the microstructure of the AlFe alloy is related with the improvements of the compressive ductility.

Effect of artificial aging time on the mechanical properties of weldment on API 5L X-52 line pipe steel

The effect of artificial aging time on the microstructure and mechanical properties in the weld and base metals of an API 5L-X52 line pipe steel was studied. Artificial aging was performed for 1000 hours at 250 °C and was monitored every 100 hours. Vickers hardness and tensile tests were used to examine the aging effect on the mechanical properties. Scanning electron microscopy and transmission electron microscopy (TEM) studies were carried out to analyze the microstructure evolution. The Vickers hardness results showed that the weld and base metals displayed a hardening tendency up to a maximum value at 500 hours of aging. The yield strength increased with aging time while the elongation-to-fracture decreased. The maximum yield strength was found at 500 hours, which was attributed to the peak-aged condition. After 500 hours, both the Vickers hardness and yield strength were reduced while the elongation was increased due to the overaging condition. The TEM observations and fracture analysis of specimens showed that the improvement of strength was associated with the nanoparticles’ precipitation, while the degradation of the microstructure and mechanical properties was related to the coarsening process of iron carbide (cementite) and niobium carbide for the weld and base metals, respectively. The largest amount of precipitation in both alloys occurred at 500 hours.

Efecto del envejecimiento natural sobre la microestructura, propiedades mecánicas, resistencia a corrosión y fractura en uniones soldadas de acero para tubería API5L X52

A characterization study was done to analyze how microstructural regions affect the mechanical properties, corrosion and fractography of the Heat Affected Zone (HAZ), weld bead and base metal for pipe naturally aged for 21 years at 30 °C. Results showed that microstructures exhibited damage and consequently decrease in properties, resulting in over-aged due to service. SEM analysis showed that base metal presented coarse ferrite grain. Tensile test indicated that microstructures showed discontinuous yield. Higher tensile strength was obtained for weld bead, which exhibited a lower impact energy in comparison to that of HAZ and base metal associated with brittle fracture by trans-granular cleavage. The degradation of properties was associated with the coarsening of nano-carbides observed through TEM images analysis, which was confirmed by SEM fractography of tensile and impact fracture surfaces. The weld bead reached the largest void density and highest susceptibility to corrosion in H2S media when compared to those of the HAZ and base metal.

Microstructural Characterization of the API X-70 Pipeline Steel Under Sour Environments

The transportation of hydrocarbides is one of the most important activities of the petroleum industry. There are many different problems related with the transportation of these products. These include stress corrosion cracking produced by H2S, sulfide stress corrosion (SSC), embrittlement by hydrogen, etc. A microstructural and chemical characterization of the API X-70 pipeline steel focus in the longitudinal weld joint was carried out. Hardness values of 120 to 185 HV were obtained in this material. Globular inclusions over all the weld bead were observed. These inclusions have a composition based mainly in iron oxide, Mn, Ca, and occasionally some sulfides. Scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) were used to study the microstructure and the chemical composition of the longitudinal weld joint and the base material. The stress corrosion cracking in the weld bead zone exposed to a NACE solution saturated with H2S has also been studied.

Microstructural and Mechanical Properties in the Weld Bead of the API X-52 Steel Pipeline.

One of the greater problems encountered in the petroleum industry including refineries and crude oil and natural gas extraction and transportation is related with the nature of the weld joining. Therefore, this work was aimed to characterize the weld beads based in the microstructure that might resemble those produced by inadequate welding. The chemical composition and mechanical properties of the weld bead, heat affected zone and the base metal were studied using SEM energy dispersive analysis (EDS) and SSRT-Slow strain rate test, respectively. Second phase particles formed by large and small globular inclusions and some irregular particles were observed. Iron oxide, Mn, Si, Al, Ca, and Mo, were the main chemical elements detected in the small inclusions. Ultimate tensile strength obtained from the SSRT tests were 395, 250, 225 MPa, for the specimens tested in air, NACE solution saturated with H2S at room temperature, and NACE solution saturated with H2S at 50°C respectively.