Cezar Henrique Gonzalez

Estudo comparativo das propriedades dinâmicas de uma liga NiTi com memória de forma e materiais estruturais clássicos

Shape Memory Alloys (SMA) are active materials that have been attracting attention due to their superior damping properties when compared to the usual structural materials. Those materials present a high damping capacity, during the phase transformation as well in martensitic phase, on low temperatures. In this work a NiTi SMA, commercial aluminum, stainless steel and brass were submitted to dynamic mechanical analysis (DMA) in single cantilever mode. Small samples in beam form were manufactured for the accomplishment of the tests. NiTi SMA studied presented a peak of damping capacity during the phase transformation, taking the damping superior values to that presented by the conventional materials. Furthermore, it was observed that the NiTi alloy presents an increase of the storage modulus during the phase transition from low temperature phase to high temperature phase, what provides a great diversity of options for technological applications for those alloys, while an almost linear decrease of stiffness was verified for the studied conventional materials.

Thermoelastic properties on Cu-Zn-Al shape memory springs

This paper present a thermomechanical study of actuators in form of helical springs made from shape memory alloy wires that can work as actuator and/or as sensor. These abilities are due to the martensitic transformation. This transformation is a diffusionless phase transition that occurs by a cooperative atomic rearrange mechanism. In this work, helical spring actuators were manufactured from Cu-Zn-Al shape memory alloy wires. The springs were submitted to constant tensile loads and thermal cycles. This procedure allows to determine thermoelastic properties of the shape memory springs. Thermomechanical properties were analyzed during 50 thermal cycles in the temperature range from 20 to 130 °C. Results of variations in critical transformation temperatures, thermoelastic strain and thermal hysteresis are discussed based on defects rearrangement and martensitic transformation theory.

Thermomechanical Analysis on Ti-Ni Shape Memory Helical Springs Under Cyclic Tensile Loads

Shape memory alloys (SMAs) present some characteristics, which make it unique material to be use in applications that require strength and shape recovery. This alloys was been used to manufacture smart actuators for mechanical industry devices and several other applications in areas as medicine, robotics, aerospace, petroleum and gas industries. However it is important to know the actuators response to external stimulus (heat source, electrical current and/or external stress) in these technological applications. This work investigated the thermomechanical behaviors of helical actuators produced from Ti-Ni alloy commercial wires. Initially, the wire was subjected to some heat treatment and characterized by differential scanning calorimeter (DSC), scanning electron microscopy (SEM), optical microscopy (OM) and Energy dispersive spectroscopy. Then two heat treatments were selected to obtain the helical actuators. The actuators were tested in an apparatus developed to apply an external traction stress in helical actuators during thermal cycles. Two wires were tested in a dynamic mechanical analyzer (DMA). The results were analyzed in comparison with thermoplastic properties obtained in thermomechanical tests. The analysis took into consideration the wiring forming process, the precipitates formation, the stress fields generated by dislocations and reorientation of martensite variants during the actuators training process.

Preparation of Metal Matrix Aluminum Alloys Composites Reinforced by Silicon Nitride and Aluminum Nitride through Powder Metallurgy Techniques

The aliminium alloys are of particular interest to both the aerospace industry and automotive industry because of their attractive combinations of properties such as medium strength, formability, weldability, corrosion resistance and low cost. Compared with a metal matrix material, significant improvements in the mechanical and physical properties such as strength, toughness, and thermal conductivity can be achievied in metal matrix composites (MMCs). In this work of investigation aluminium alloy AA6061 was reinforced by 5, 10 and 15% (in mass %) of Si3N4 (silicon nitride) and AlN (aluminium nitride) by mechanical alloying in a vibratory type SPEX mill, cold uniaxial compaction and vacuum sitering in order to investigate the influence of the particulate phase in the microstructure and mechanical properties of the composites obtained. The microstructure of the powders and the sintered materials were evaluated by means of SEM and the hardness and were evaluated by hardness test.

Manufacturing and Characterization of AA1100 Aluminum Alloy Metal Matrix Composites Reinforced by Silicon Carbide and Alumina Processed by Powder Metallurgy

Powder Metallurgy (PM) Techniques consists in a suitable technique to process composites materials. A specific PM technique of mechanical alloying developed to produce new materials in the solid state is a consolidated route to obtain aluminum alloys metal matrix composites. Aluminum alloys metal matrix composites allies the good properties of aluminum and its alloys but with poor mechanical properties and the reinforcement of ceramics phases which add better mechanical properties to these alloys. The research of this materials processing by PM techniques presented new materials with improved properties. In this work an AA1100 aluminum alloy was reinforced by particulate silicon carbide and alumina types of ceramic phases. The powders were mixed and then processed by mechanical alloying in a SPEX vibratory type mill. Then the powders obtained were compacted and vacuum sintered. The sintered composites were characterized by means of Scanning Electron Microscopy (SEM) plus Energy Dispersive Spectroscopy (EDS) and Vickers hardness (HV) tests to evaluate the mechanical behavior.

Effect of Spun Velocities and Composition on the Microstructure and Transformation Temperatures of TiNi Shape Memory Ribbons

Ti‒50.13Ni and Ti‒49.62Ni (at.%) shape memory alloy ribbons were fabricated by melt-spinning method at different circumferential wheel velocities. The effects of wheel velocity, chemical composition and heat treatments on microstructure and Transformation temperature were investigated. Differences in wheel velocity led to differences in cooling rate and sample dimension, as well as in phase transformation temperatures. Two heat treatment conditions were studied, 350°C for 1h and 350°C for 5h. In the samples produced at high wheel velocity and heat-treated at 350°C for 5h, nanosized Ti-rich precipitates were observed in both chemical compositions. Cross-sectional microstructure was studied by optical microscopy; SEM was used to study the nanometric grains and nano precipitation. The transformation temperatures were analyzed by DSC.

Preparation of Molybdenum High Speed Tool Steels with Addition of Niobium Carbide by Powder Metallurgy Techniques

High speed steels processed by Powder Metallurgy (PM) techniques present better mechanical properties when compared with similar steels obtained by the conventional process of cast to ingot and hot working. PM techniques produce improved microstructures with smaller and better distribution of carbides. Liquid phase sintering high speed steel seems to be a cheaper processing route in the manufacturing of tool steels if compared to the well-known and expansive hot isostatic pressing high speed steels. The introduction of niobium as alloying element began with the object of replacing elements like vanadium (V) and tungsten (W). Phase liquid sintering consists in a manufacturing technique to process high speed steels by powder metallurgy. The aim of this work of research is to process and obtain AISI M2 and M3:2 with and without the addition of niobium carbide by high energy milling, cold uniaxial compaction and vacuum sintering in the presence of a liquid phase. The powders of the AISI M2 and M3:2 were processed by high energy milling adding a small quantity of niobium carbide (6% in mass), then the powders were characterized by means of X-ray diffraction (XRD) and scanning electron Microscopy (SEM) plus energy dispersion spectroscopy (EDS) in order to evaluate the milling process. The powders of the AISI M2 and M3:2 with the addition of niobium carbide (NbC) were uniaxially cold compacted and then submitted to vacuum sintering. The sintered samples had their microstructure, porosity and carbide distribution observed and evaluated by means of Scanning Electron Microscopy (SEM) and the mechanical property of hardness was investigated by means of Vickers hardness tests. At least five samples of each steel were investigated.

Precipitates Formation in Ti-Ni Equiatomic Alloys due to Annealing Heat Treatment

The use of smart material such as Ti-Ni in actuators application requires an intense mechanical and metallurgical investigation to understand its behavior. This paper studies martensitic transformation using DSC and X-ray diffraction techniques to compare shape memory parameters in Ti-50.2%Ni (A1) and equiatomic Ti-50.0%Ni (A2) Alloys. The as as-received samples were submitted to annealing at 400°C and 500°C for 24 hours then quenched in at 25°C. The influence of heat treatment on martensitic transformations temperatures and the appearance of R-phase were analyzed using DSC and X-ray diffraction.

Processing of AISI M2 HSS with Addition of NbC by Mechanical Alloying Using two Different Types of Attritor Mills

The processing of a molybdenum AISI M2 high speed steel with the addition of NbC (6% in mass) by a Powder Metallurgy technique of Mechanical Alloying is the aim of this work. Mechanical Alloying (MA) has been used primarily for particle size reduction, to its present status as an important method for the preparation of either materials with enhanced physical and mechanical properties or, indeed, new phases, or new engineering materials. In this work, niobium carbide (NbC) was added to the AISI M2 HSS powders by Mechanical Alloying technique in two different types of attritor mills and the materials which resulted were characterized by means of SEM plus EDS. The powders were processed in a horizontal attritor Zoz mill and in a vertical attritor mill developed in our laboratory. The parameters of milling were distinct and the results of the processing were compared.

Secondary Hardening of an AISI M3:2 High Speed Steel Sinter 23 Hot Isostatic Pressed

The main aim of this work was to study the behavior of the secondary hardening of AISI M3:2 high speed steel named Sinter 23® produced by powder metallurgy process of hot isostatic pressing (HIP). The M3:2 high speed steel Sinter 23® was submitted to heat treatment of hardening with austenitizing temperatures of 1140 oC, 1160 oC, 1180 oC and 1200 oC and tempering at 540 oC, 560 oC and finally 580 oC. The effectiveness and response of the heat treatment was determined using hardness tests (Vickers and Rockwell C hardness) and had its property of secondary hardness evaluated. The results showed that the secondary hardening peak of Sinter 23® high speed steel (tempering temperature at which maximum hardness is attained) is at 540 °C for the lower austenitization temperatures of 1140 °C and 1160 °C, and it is at 560 °C for the higher austenitizing/quenching temperatures of 1180 °C and 1200°C.