Materials Science Forum Vols. 530-531

Abstract: Mechanical alloying and mechanical fine grinding processes are mostly based on the high energy milling technique. Equipment of a horizontal high-energy ball mill that has been developed in the Cefet-BA is a low cost machine with high performance. These milling machines are equipped with a cylindrical stainless steel horizontal container. Inside the container, a chamber of water circulation is used to maintain, powdered materials, the room temperature. The grinding container inside to chamber horizontal container is a container, cylindrical stainless steel, opened of the two sides. The container with the powder particles is a sealed of two sides and vacuum out-gassed is realized. A motor driven rotor is used to accelerate the grinding media and the milling process is realized due to the ball to ball/rotor/wall impacts as their kinetic energy is transferred into the powder which is randomly located between the colliding balls. The rotor milling machine equipment permits two rpm e.g. 500 and 1500 rpm. Machines based on this design from lab scale (3.0 liter volume), mainly to develop new powders and materials.

Abstract: The present work reports on the preparation of the Ta5SiB2 compound by highenergy ball milling and subsequent heat treatment from elemental Ta-12.5at%Si-25at%B powder mixture. The milling process was carried out at room temperature in a planetary ball mill under argon atmosphere. Following the milling process, the powders were heat-treated at 1200oC for 4h under Ar atmosphere in order to obtain the equilibrium microstructure. The milled and heat-treated powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated that the Si peaks disappeared after milling for 1h. It was noted that the broadening and the reduced intensity of Ta peaks occurred continuously up to milling for 10h, suggesting that the Si and B atoms were preferentially dissolved into the Ta lattice during ball milling to form a supersaturated solid solution. A halo was formed in Ta-12.5at%Si-25at%B powders milled for 100h, suggesting that an amorphous phase was achieved. No intermetallic phase was formed in powders milled for 200h. A large amount of Ta5SiB2 was formed after heat treatment at 1200oC for 4h. In addition, peaks of TaB and another unknown phase were also identified.

Abstract: This work reports on the preparation of Ni-50Ti and Ni-40Ti-10Nb and Ni-30Ti- 20Nb (at.%) powders by high-energy ball milling and subsequent heat treatment. The milling process was carried out at room temperature in a planetary ball mill under Ar atmosphere. The as-milled powders were than heat-treated at 900oC for 1h under Ar atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), and microanalysis via energy dispersive spectroscopy (EDS) were used to characterize the milled and heat-treated powders. A metastable phase was initially formed in Ni-50Ti and Ni-40Ti-10Nb powders milled for 1h. Following the ball milling, the B2-NiTi compound was formed in these powder mixtures. The disordering of the B2-NiTi compound occurred owing the internal lattice strain after milling for 30h. Two phases were identified in Ni-50Ti and Ni-40Ti-10Nb powders milled for 60h: the metastable phase previously reported, and an amorphous phase. In Ni-30Ti-20Nb powders, it was noted the presence of an amorphous halo only. A structural relaxation of the B2-NiTi phase occurred in heat-treated Ni-50Ti, Ni-40Ti-10Nb, and Ni-30Ti-20Nb powders. A small amount of Ni3Ti and NiTi2 was also formed after heat treatment at 900oC for 1h, and an iron contamination lower than 2at.% was found.

Abstract: The aim of this work is to prepare the Ni3Ti, NiTi, and NiTi2 compounds by mechanical alloying from elemental Ni-25at.%Ti, Ni-50at.%Ti, and Ni-66.6at.%Ti powder mixtures. The milling process was carried out in a planetary ball mill under argon atmosphere using a rotary speed of 200rpm, stainless steel balls (10 and 19 mm diameters) and vials (225mL), and a ball-to-powder weight ratio of 10:1. Following, the milled powders were heat treated at 900oC for 1h in order to attain the equilibrium microstructures. The milled powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and microanalysis via EDS. Similar ball milling behavior of Ni-Ti powders was noted in this work, e.g., a pronounced cold-welding between ductile powders occurred during the initial milling times. The Ni3Ti, NiTi, and NiTi2 compounds were synthesized after milling for 30h. Atomic disordering of the NiTi and NiTi2 compounds was achieved, and amorphous structures were then formed in Ni-50Ti e Ni-66.6Ti powders milled for 60h and 210h, respectively. Homogeneous matrixes constituted by the Ni3Ti, NiTi, and NiTi2 phases were formed in Ni-Ti powders after heat treatments at 900oC for 1h. Iron contamination lower than 2 at-% was measured by EDS analysis in heat-treated Ni-Ti alloys.

Abstract: this paper describes the PADS process and equipment, which has been developed to produce PIM components. The use of a hybrid system of plasma discharge and Mo heating elements makes debinding and sintering PIM components in the same heating cycle possible. The use of an abnormal discharge between a cathode and anode under low-pressure provides reactive specimens that break the polymeric chains of the binder of the molded parts. By the combination of these features it was possible to use heating rates of 2,0º C/min during the debinding step. The hydrocarbons, resulted from debinding, are pumped out through vacuum pumps, without traps. The clean environment makes possible to sinter the parts in the same cycle, as well as execute a surface treatment during cooling. The results present short process times as 6 hours to Fe2Ni0,6C low alloy steel and 7 hours to 316-L stainless steel. Characteristics as density, carbon content and mechanical properties are similar to traditional PIM process. The reduction of energy and gas consumption and shorter lead-times are economic advantages of PADS system. The clean environment of PADS is also an ecological advantage.

Abstract: Aiming to obtain components with higher density, this work evaluated the technical and economical viabilities to replace the pre-alloyed Fe49Co2V by an elemental powder alloy of iron and cobalt (Fe-50Co). Using an elemental alloy could increase the density of the final material due to the driving force created by the chemical gradient between the powders. The results showed that is possible to achieve higher densities in an elemental powder Fe-50Co alloy sinterized at the same temperature and in shorter times than the Fe49Co2V alloy. The analysis of economical viability showed that the replacement of the alloys have advantages as the pre-alloyed powder price is higher than the elemental.

Abstract: A new development in MIM aims at the manufacturing of parts out of two materials, the Two Components Injection Molding, which allows the production of parts with different materials in distinct locations, obtaining different properties in distinct regions of the part. In this work an austenitic stainless steel was combined with tool steel, based on the Two Components Injection Molding process, using dilatometric experiments to analyze the behaviour of materials during sintering. Metallographic analyses and tensile tests were made to verify the microstructure and the strength in the contact area of the two materials.

Abstract: Investigations of composite materials based on EN AW-Al Cu4Mg1(A) aluminum alloy reinforced with the Ti(C,N) particles with various weight ratios of 5, 10, and 15% are presented. Powders of the starting materials were mixed in the laboratory vibratory ball mill to acquire the uniform distribution of reinforcement particles in the matrix material. The components were initially compacted at cold state in a die with the diameter of ∅ 26 mm in the laboratory vertical unidirectional press – with a capacity of 350 kN. The obtained P/M compacts were heated to a temperature of 480÷500°C and finally extruded – with the extrusion pressure of 500 kN. Bars with a diameter of 8 mm were obtained as the end product. Based on the microstructural examinations of the obtained composite materials, the uniform distribution of the reinforcing particles in the aluminum matrix was revealed. Hardness tests, tensile tests and the ultimate compressive strength tests made it possible demonstrate that all these properties change along with the reinforcing particles concentration change.

Abstract: Mechanical alloying (MA) has been successfully used to produce alloys and composites with a high homogeneity degree. In current research, titanium (Ti) powder was mixed with 40, 50% volume of hydroxyapatite (HAp). MA was performed without atmosphere control, at room temperature, for 4.5 hours of milling time, at rotation speed of 300 rpm. Samples of material were compacted in cylindrical form at 350 MPa and sintered in 2.0 flux air (l/min) at 1000, 1100 and 1200oC during 1 hr. The material’s morphological and microstructural characterization, in powder form and in sintered material, was performed by scanning electronic microscope and X-ray diffractometry. Thermal treatments revealed that sintering temperature affects the microstructure, microhardness and the composition of the composites evaluated by EDS.