Andersan dos Santos Paula

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 0xa0°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-51xa0at.%Ti), after being subjected to an initial heat treatment at 500xa0°C for 30xa0min in air followed by multiple steps of marforming (cold rolling, 30% thickness reduction) intercalated with heat treatments at 500xa0°C for 30xa0min in air and a final heat treatment at four different temperatures (400, 450, 500, and 600xa0°C) for 30xa0min 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.

The Influence of Sample Preparation on the Quantitative Analysis of the Volume Fraction of Martensite Formed in a 304l Trip Steel

The metastable 304L austenitic stainless steels are susceptible to phase transformation induced by plastic deformation. The traditional metallographic preparation, via mechanical methods, introduces superficial plastic deformation from grinding and polishing. It is important to evaluate this effect on the results of quantitative analysis of martensite formed in 304L steels and similar alloys. In this work, phase transformation was induced by a tensile test at room temperature with two different plastic deformation rates in order to provide distinct structural conditions for the proposed analysis. X-ray Diffraction (XRD) and Ferritescopy were used to determine the volume fraction of martensite in samples with and without metallographic preparation. The results show that the analyses quantitative were not affected by metallographic preparation.

Microstructural Characterization and Evaluation of Mechanical Properties of Steel with Different Biphasic Microstructures Obtained from LNE 500 Steel

In this work was carried out the microstructural characterization and evaluation of mechanical properties of steel with different microstructures. The intercritical region and the existing phases in function of temperature were determined using the THERMOCALC software. The samples of steel were quenched at different temperatures to obtain differents microstructures consisting of ferrite, pearlite and martensite. The microstructural characterization of the samples was performed by qualitative and quantitative metallography. The determination of volume was performed with the Image J software. The mechanical properties were determined by uniaxial stress test, which determined the parameters: yield strength, tensile strength, breaking point and total elongation.

The Influence of Different Microstructures to Fracture Toughness and Hardness of Quenched LNE 380 Steel at Different Temperatures

In this work it was analyzed the evolution of mechanical properties of Dual-Phase steel as a function of volume fractions of ferrite and martensite, obtained from steel type LNE 380. The intercritical region and the existing phases in function of temperature were determined using the THERMOCALC software. The samples of steel were quenched at different temperatures to obtain differents microstructures consisting of ferrite, pearlite and martensite. The microstructural characterization of the samples was performed by qualitative and quantitative metallography. The mechanical properties were determined by hardness and impact tests. It was concluded that the volume fraction of ferrite and martensite calculated experimentally agrees with the simulation and the variation of these fractions affects significantly the hardness of the steel, but does not significantly affect the results of fracture toughness.

Textural Evolution Evaluated by EBSD and XRD after Thermal Treatment in Ni-Ti Shape Memory Alloy

The Nickel-Titanium (Ni-Ti) alloys are the most attractive amongst shape memory alloys (SMA) due to their good functional properties coupled with high strength and good ductility. The transformation temperatures in Ni-Ti SMA can be altered by chemical composition and thermal and/or mechanical treatments adequate to obtain reversible martensitic transformation in one or more steps. The goal of the present work is to investigate the evolution of texture in Ni-Rich Ni-Ti (50.8at%Ni-Ti) SMA showing different phase transformation temperatures as a result of different thermal/mechanical history: straight-annealed (as-received condition) and subsequent thermal treatment at 500°C for 30 minutes in air. The microstructural and textural results were obtained by Electron Backscattering Diffraction on Scanning Electronic Microscopy (ESBD/SEM) and by X Ray Diffraction (XRD) at room temperature. Mechanical properties were measured by Vickers micro hardness tests at room temperature.