Materials Science Forum Vols. 727-728

Abstract: This paper reports on the phase transformation during the preparation of Ni-25Nb, Ni-25Ta, Ni-20Nb-5Ta and Ni-15Nb-10Ta (at-%) powders by high-energy ball milling from elemental powders. The milling process was performed in a planetary ball milling using stainless steel balls and vials, rotary speed of 300rpm, and a ball-to-powder of 10:1. To minimize contamination and spontaneous ignition the powders were handled under argon atmosphere in a glove box. The milled powders were characterized by means of X-ray diffraction techniques. Results indicated that the Ni atoms were preferentially dissolved into the Nb (and/or Ta) lattice at the initial milling times, which contributed to change the relative intensity on the diffraction peaks. After the dissolution of Nb (and/or Ta) into the Ni lattice, the Ni peaks were moved to the direction of lower diffraction angles in Ni-25Nb, Ni-25Ta, Ni-20Nb-5Ta, Ni-15Nb-10Ta powders, indicating that the mechanical alloying was achieved. .

Abstract: This work discusses on the structural evaluation of mechanically alloyed and heat-treated Ti-25at%Si powders. The milling process was conducted in a planetary ball mill using stainless steel balls/vials, 200 rpm and ball-to-powder weight ratio of 5:1, whereas the heat treatment was conducted under Ar atmosphere at 1100°C for 4 h. Samples were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and energy dispersive spectrometry. The Si peaks disappeared after milling for 30h, indicating that the Si atoms were dissolved into the Ti lattice in order to form an extended solid solution. The Ti peaks were broadened and their intensities reduced for longer milling times whereas a halo was formed in Ti-25Si powders milled for 200h suggesting that an amorphous structure was achieved. The crystallite size was decreased with increasing milling times. A large Ti₃Si amount was found in mechanically alloyed Ti-25at%Si powders after heating at 1100°C for 4h.

Abstract: This work discusses on the preparation of Ni-45Ti-5Mo, Ni-40Ti-10Mo and Ni-46Ti-2Mo-2Zr (at-%) alloys by high-energy ball milling and hot pressing, which are potentially attractive for dental and medical applications. The milling process was performed in stainless steel balls (19mm diameter) and vials (225 mL) using a rotary speed of 300rpm and a ball-to-powder weight ratio of 10:1. Hot pressing under vacuum was performed in a BN-coated graphite crucible at 900°C for 1 h using a load of 20 MPa. The milled and hot-pressed materials were characterized by X-ray diffraction, electron scanning microscopy, and electron dispersive spectrometry. Peaks of B2-NiTi and Ni₄Ti₃ were identified in XRD patterns of Ni-45Ti-5Mo, Ni-40Ti-10Mo and Ni-46Ti-2Mo-2Zr powders milled for 1h. The NiTi compound dissolved small Mo amounts lower than 4 at%, which were measured by EDS analysis. Moreover, it was identified the existence of an unknown Mo-rich phase in microstructures of the hot-pressed Ni-Ti-Mo alloys.

Abstract: This work evaluates the influence of particle morphology in mixture rheology. Range of particle morphology was used, changing in the mixtures the proportion of spherical powders and irregular powders, respectively gas and water atomized powders, in fraction of 0, 25, 50, 75 and 100% in mass. Components were obtained by mixtures with solid loading very close to critical values. Rheological analysis of the mixtures was elaborated in a capillary rheometry. The solids loading maximum was larger in 10% for the mixtures with only gas atomized powder, when compared to the mixture with just water atomized powder. The mixtures between gas and water atomized powders with maximum solid loading present difficulties in obtaining homogeneity and presents high viscosity.

Abstract: Powder Injection Molding allows processing of multifunctional parts through combination of different materials in a single structure. This technique so-called Two Components Powder Injection Molding has been developed some years ago and now is rapidly being considered for many engineering applications. In this paper, some important aspects of materials selection and processing conditions are reviewed in order to look insight of the technology. To show how successful can be the technique, carbonyl iron feedstock was co-sintered to the recently developed self-lubricating steel, aiming at different tribological properties in each side of the final component. Defect-free parts were obtained and the tensile resistance was in the same range of single material parts, representing a very strong bonding interface.

Abstract: Joining materials with different properties into a single component is an attractive solution that allows producing parts with unique properties. In this respect, Two-Component Metal Injection Moulding (2C-MIM) presents numerous advantages, since the moulding and joining stage are performed in a single process step. In this work, the challenges, which occur when different materials are combined, are elucidated. Furthermore, the contact between metals with unequal chemical compositions leads to atomic interdiffusion that forms an interface layer. The interface quality is crucial to the production of intact parts after processing. Different material combinations are co-sintered and the interfaces are characterized by means of optical microscopy and EDX/SEM line scans. Further, thermodynamic and kinetic simulations are used to examine the interdiffusion in detail. The results show promising possibilities to combine different materials and helpful methods to examine the interface.

Abstract: Composites are combinations of two materials in which one of the materials, called the reinforcing phase, is in the form of fibers, sheets, or particles and is embedded in the other materials called the matrix phase. If the composite is designed and fabricated correctly, it combines the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material. In this work of research aluminium alloy AA6061 was reinforced by 5, 10 and 15% (in mass %) of SiC and Al₂O₃ by mechanical alloying in a vibratory type SPEX mill, cold uniaxial compaction and vacuum sintering 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 SEM and the hardness was evaluated by hardness tests.

Abstract: 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.

Abstract: This work aims to synthesize combustion reaction, functionalized with chitosan nanoparticles and characterize ZnAl_1.94(Yb:Er)_0.06O₄, codoped with x = 0.06 mol in the proportion 5:1 of Yb:Er. Nanoparticles before and after functionalization were characterized by XRD, TGA/DTA, FTIR and SEM. The results show that before and after functionalization presented ZnAl₂O₄ majority phase and Al₂Yb₄O as secondary phase. Multiple bands around 1100 cm^-1 and 1040 cm^-1 corresponding to the asymmetric stretching Si-O confirms the functionalization of nanoparticles. Nanoparticles presented before functionalization morphology heterogeneous, consisting of clusters of particles with near-spherical shape, large particle size distribution, consisting of large clusters with size around 3 µm and smaller clusters in the shape of plates with size in order of 0.5 µm. After functionalization, the morphology shows the formation of a film consisting of amorphous phase and crystalline phase. The mass loss for the nanoparticles before and after functionalization was 7.2 and 39%, respectively.

Abstract: Typically, diamond tools produced by Powder Metallurgy are very effective in cutting processes in general, because are used diamond composites for cutting action. In these tools, diamond abrasive grains are embedded in the metal matrix. Some of the most common examples of these tools are the cutting discs, abrasive crowns, drills and diamond wires. This work studies the Fe-Cu-Co-diamonds composites processed by the powder metallurgy techniques powders mixing and hot pressing at 850°C/35MPa/3 min. Microstructural analysis of composites as well as metal matrix-diamond adhesion was made by scanning electron microscopy-SEM after abrasion resistance tests. Compression tests were carried out to evaluate the elastic properties of composites, i.e., modulus of elasticity (E) and yield stress (σ_e), aiming at the assessment of the metal matrix-diamond adhesion. It was found satisfactory adhesion for the composites M2 and M3, with values σ_e = 360 MPa and 375 MPa, respectively. Keywords: diamond tools, powder metallurgy, composite Fe-Cu-Co-diamond.