Mechanical characterization of PM aluminum composites by small punch test

In this work Small Punch Test (SPT) was applied to study the mechanical behavior of ultrafine-grained Al-Al2O3metal matrix composites (MMCs) fabricated in situ via powder metallurgy route (HITEMAL®). SuchMMCs show attractive mechanical properties, enhanced creep performance and increased thermal stability atelevated temperatures, not normally associated with service of conventional Al alloys, even after prolongedhigh temperature exposure. MMCs fabricated from two powders of different particle size (d50 = 8.9 and1.2μm) were evaluated in the present work.SPT was performed at room temperature using disc-shaped specimens of 10 mm in diameter. Theeffect of the different disc thickness (0.4, 0.5 and 0.6 mm) on the load vs. displacement function wasevaluated. The displacements monitored from top and bottom sites of the specimen varied during the courseof the test. The discs deformed throughout the test by two plastic stages, typical for ductile materials. Therelation between load-displacement and stress–strain tensile curves for both composites was analyzed. Adrastic change of mechanical behavior between the green compact of cold pressed material and the hot forgedmaterial was detected.New methods of determination of a characteristic load PY, which represents a transition from elastic toplastic bending regime were presented and discussed. A relationship between PY and corresponding yieldstress was studied for each composite material by a calculation of their respective correlation parameters.Keywords: Small punch test, powder metallurgy, yield strength, aluminum, composite, correlation parameter

Effects of Wire EDM on the Microstructure of P/M Titanium Samples

Komercijalno čisti titanij (CP Ti) se koristi u dentalnoj medicini zbog biokompatibilnosti, dobrih mehaničkih svojstava i otpornosti na koroziju. Konvencionalni proizvodni procesi izrade takvog titanija mogu utjecati na kvalitetu površine uzoraka i rezultirati slabim vezanjem CP Ti s dentalnom keramikom. Zato se uvode nove tehnologije proizvodnje titanija, primjerice metalurgija praha i oblikovanje na erozimatu s žicom (WEDM). Svrha ovog istraživanja jest odrediti utjecaj WEDM-a na površinu uzoraka P/M CP Ti proizvedenih za ispitivanje vezne čvrstoće prema normi ISO 9693. Materijali i metode: Osam uzoraka P/M CP Ti dimenzija prema normi ISO 9693 proizvedeno je korištenjem WEDM-a i podijeljeno u dvije grupe – u neobrađene i brušene. Površine obje grupe uzoraka analizirane su metodama SEM, EDS i XDR. Rezultati: Analize neobrađenih uzoraka metodama SEM i EDS pokazuju tanki sloj različitog sastava i frakture. Brušeni uzorci imaju homogenu strukturu bez fraktura. Analiza metodom XDR pokazuje visoku koncentraciju titanijevih oksida na površini neobrađenih uzoraka, a nakon brušenja dobivena je samo čista α-faza. Zaključak: WEDM je metoda prikladna za proizvodnju uzoraka prema normi ISO 9693, ako se uzorci naknadno bruse.Purpose: Commercially pure titanium (CP Ti) has been recognized in dentistry for its biocompatibility, good mechanical properties and corrosion resistance. Conventional manufacturing processes can affect surface quality and result in poor bonding of dental ceramics to CP Ti. This is why powder metallurgy (P/M) and wire electro-discharge machining (WEDM) are being introduced in the manufacturing process. The aim of this study was to evaluate the effect of WEDM on the surface composition and microstructure of P/M CP Ti samples produced for bond strength testing according to ISO 9693. Materials and methods: Eight samples of P/M CP Ti, dimensions according to ISO 9693, were made using WEDM and divided in two groups (untreated and grinded). Microanalyses of chemical composition and microstructure of both groups were made using SEM, EDS and XDR. Results: SEM and EDS analysis of untreated samples showed a thin layer on surfaces with fractures in it. Grinded samples showed homogenous structure with no layer and no fractures. XDR analysis showed high level of oxides on the surface of untreated samples, while after grinding only pure α-phase was found. Conclusion: WEDM is a suitable method of sample production for ISO 9693 if accompanied by grinding with silicon carbide papers P320-P4000

SAP-like ultrafine-grained Al composites dispersion strengthened with nanometric AlN

This paper reports the development of novel Sinter-Aluminum-Pulver (SAP)-like Al-AlN nanocomposites via replacing the native AlO thin films on fine Al powder with a large volume fraction of in situ formed nanometric AlN dispersoids. Fine gas-atomized Al powder (d=1.3μm) compacts were first partially nitrided at 590°C in flowing nitrogen, controlled by a small addition of Sn (0.3-0.4wt%), and subsequently consolidated by hot direct extrusion. The resulting Al-AlN composites consisted of submicrometric Al grains reinforced with nanometric AlN dispersoids together with some nanometric AlO dispersoids. An Al-13vol% AlN nanocomposite fabricated this way achieved exceptional ultimate tensile strength of 227MPa, yield strength of 195MPa and Young's modulus of 66GPa at 300°C, superior to typical SAP materials and coarse grained Al-AlN composites. In addition, the Al-13vol% AlN nanocomposite exhibited good thermal stability up to 500°C. The strengthening mechanism is discussed

Ultrafine-grained Al composites reinforced with in-situ Al3Ti filaments

Ultrafine-grained (UFG) Al matrix composites reinforced with 15 and 30vol% in-situ Al3Ti filaments were fabricated by extrusion of Al-Ti powder mixtures followed by solid-state reactive diffusion. Fine Al powder particles (1.3μm) heavily deformed the coarser Ti particles (24.5μm) into filaments during extrusion. Upon a subsequent operation of hot isostatic pressing (HIP), the micrometric Al3Ti filaments elongated along the extrusion direction and formed in situ in the UFG Al matrix. Fabricated composites are free of pores and voids with perfect bonding created at the Al-Al3Ti interfaces. In parallel, a small portion (2.4vol%) of nanoscale γ-Al2O3 particles, which originate from native amorphous films on fine Al powders, formed in situ and were homogenously dispersed in the Al matrix. The microstructures of as-extruded and after HIP composites were analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and electron back-scattered diffraction (EBSD). Owing to the presence of nanometric γ-Al2O3 particles with Al high angle grain boundaries (HAGBs), the UFG Al matrix remained stable even after HIP at 600°C for 9h. The mechanical properties and creep performance of composites at testing temperatures of up to 600°C were systematically studied. The Al-Al3Ti composites exhibited a combination of increased strength and Young's modulus in addition to excellent creep performance and structural stability, which indicates that the studied composites are potential structural materials capable of service at elevated temperatures.Fil: Krizik, Peter. Slovak Academy of Sciences; EslovaquiaFil: Balog, Martin. Slovak Academy of Sciences; EslovaquiaFil: Nosko, Martin. Slovak Academy of Sciences; EslovaquiaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Dvorak, Jiri. Institute of Physics of Materials; República ChecaFil: Bajana, Oto. Slovak Academy of Sciences; Eslovaqui

Forged HITEMAL: Al-based MMCs strengthened with nanometric thick Al2O3 skeleton

Bulk Al-Al2O3 metal matrix composites (MMCs) named HITEMAL (high temperature aluminum) were fabricated in situ by forging compaction of five different types of gas-atomized commercial purity Al powders with a mean particle size in the range of 1-9μm. As-forged HITEMAL consisted of (sub)micrometric Al grains (matrix) decorated with nanometric thick amorphous Al2O3 (a-Al2O3) skeleton. Low-angle grain boundaries (LAGBs) free of Al2O3 were located in the Al grain interior. The Al grain size and the portion of LAGBs increased with the increase in the relative powder surface area. As-forged HITEMAL shows excellent thermal stability up to 400°C for 24h. Annealing at temperatures ≥450°C led to crystallization and morphological transformation from a-Al2O3 skeleton to nanometric γ-Al2O3 particles. Owing to the pinning effect of Al2O3 phase, no Al grain growth took place during annealing up to 500°C. HITEMAL showed attractive mechanical properties especially when tested at 300°C (yield strength up to 220MPa, Young's modulus up to 58GPa). Despite the presence of a nearly continuous a-Al2O3 skeleton along adjacent Al grains, forged HITEMAL materials had reasonable room temperature elongation of 7-26%. HITEMAL's elongation decreased as the Al grain size decreased and with increased testing temperature. The loss in elongation (uniform and total) was attributed to the inhomogeneous flow, which occurred due to high densities of high angle grain boundaries (dislocation sinks) and small content of LAGBs. The strength of HITEMAL stemmed from grain boundary mediated strengthening mechanisms. The results showed a positive deviation from the Hall-Petch plot, which is typical behavior of ultrafine-grained metals. Transformation of a-Al2O3 skeleton to γ-Al2O3 particles led to deterioration of the HITEMAL strength and Young's modulus.Fil: Balog, Martin. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Krizik, Peter. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Nosko, Martin. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Hajovska, Zuzana. Slovak Academy of Sciences. Institute of Botany; EslovaquiaFil: Castro Riglos, Maria Victoria. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Rajner, Walter. No especifíca;Fil: Liu, De Shin. No especifíca;Fil: Simancik, Frantisek. Slovak Academy of Sciences. Institute of Botany; Eslovaqui

On the thermal stability of ultrafine-grained Al stabilized by in-situ amorphous Al2O3 network

Bulk Al materials with average grain sizes of 0.47 and 2.4μm, were fabricated by quasi-isostatic forging consolidation of two types of Al powders with average particle sizes of 1.3 and 8.9μm, respectively. By utilizing the native amorphous Al2O3 (am-Al2O3) film on the Al powders surfaces, a continuous, ~7nm thick, am-Al2O3 network was formed in situ in the Al specimens. Systematic investigation of the changes to the am-Al2O3 network embedded in the Al matrix upon heating and annealing up to 600°C was performed by transmission electron microscopy (TEM). At the same time, the stability of the Al grain structure was studied by transmission Kikuchi diffraction (TKD), electron back-scatter diffraction (EBSD), and TEM. The am-Al2O3 network remained stable after annealing at 400°C for 24h. In-situ TEM studies revealed that at temperatures ≥450°C, phase transformation of the am-Al2O3 network to crystalline γ-Al2O3 particles occurred. After annealing at 600°C for 24h the transformation was completed, whereby only nanometric γ-Al2O3 particles with an average size of 28nm resided on the high angle grain boundaries of Al. Due to the pinning effect of γ-Al2O3, the Al grain and subgrain structures remained unchanged during annealing up to 600°C for 24h. The effect of the am-Al2O3→γ-Al2O3 transformation on the mechanical properties of ultrafine- and fine-grained Al is discussed from the standpoint of the underlying mechanisms.Fil: Balog, Martin. Slovak Academy of Sciences; Eslovaquia. University of California at Davis; Estados UnidosFil: Hu, Tao. University of California at Davis; Estados UnidosFil: Krizik, Peter. Slovak Academy of Sciences; EslovaquiaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Saller, Brandon D.. University of California at Davis; Estados UnidosFil: Yang, Hanry. University of California at Davis; Estados UnidosFil: Schoenung, Julie M.. University of California at Davis; Estados UnidosFil: Lavernia, Enrique J.. University of California at Davis; Estados Unido

Dispersion and Preparation of Nano-AlN/AA6061 Composites by Pressure Infiltration Method

Nanomaterials play an important role in metal matrix composites (MMC). In this study, 3.0 wt.%, 6.0 wt.%, and 9.0 wt.% nano-AlN-particles-reinforced AA6061 (nano-AlN/AA6061) composites were successfully prepared by pressure infiltration technique and then hot extruded (HE) at 500 °C. The microstructural characterization of the composites after HE show that the grain structure of the Al matrix is significantly refined, varying from 2 to 20 μm down to 1 to 3 μm. Nano-AlN particles in the composites are agglomerated around the matrix, and the distribution of nano-AlN is improved after HE. The interface between AA6061 and nano-AlN is clean and smooth, without interface reaction products. The 3.0 wt.% nano-AlN/AA6061 composite shows an uppermost yield and supreme tensile strength of 333 MPa and 445 MPa, respectively. The results show that the deformation procedure of the composite is beneficial to the further dispersion of nano-AlN particles and improves the strength of nano-AlN/AA6061 composite. At the same time, the strengthening mechanism active in the composites was discussed