Materials Science Forum Vol. 879

Abstract: The effects of Al on the monotonic deformation behavior of Fe-Mn-C twinning-induced plasticity (TWIP) steels have been extensively investigated; however, how the addition of Al affects the fatigue properties of these steels is unknown. The present paper deals with the cyclic deformation properties of Fe-22Mn-0.6C-0Al and Fe-22Mn-0.6C-3Al steels by means of total strain-controlled low-cycle fatigue tests. The total strain amplitude ranges from 0.002 to 0.01. The evolved microstructures of fatigued samples were observed by transmission electron microscopy. Results show that the addition of Al has a significant effect on the cyclic deformation behavior, fatigue lifetime and evolved microstructure of Fe-Mn-C TWIP steel.

Abstract: In precipitation strengthened ferritic alloys, the Fe-Cu binary system is a well-studied model system. Still, many unsettled questions remain about the early stages of bcc Cu precipitation, most of which refer to the shape and composition of the critical and post-critical nuclei. Since the critical nucleation states are hard to investigate by experimental methods, we propose a computational strategy to reconstruct precipitation pathways and identify the nucleation states making use of Monte Carlo simulations combined with Rare Event Sampling methods. The precipitation process is reproduced by Monte Carlo simulations with an energy description based on the Local Chemical Environment approach, applying efficient pair potentials, which are dependent on the chemical environment, and the Forward Flux Sampling technique. This method provides profound insight into the shape and composition of the early-stage precipitates and also the critical cluster size and shape in dependency of the temperature and supersaturation.

Abstract: Controlled diffusion solidification (CDS) is a novel and simple process that enables the formation of non-dendritic microstructure of primary Al phase through mixing two liquid alloys of different composition and temperature together. A quaternary alloy (Al-5.0Cu-0.35Mn-0.25Ti, wt.%), having a similar chemical component with ZL205A, was fabricated using controlled diffusion solidification (CDS) method with different mixing temperature. The mixing temperature of two liquids mostly affects the cast structure especially the primary Al phase. Results show that CDS can reduce the element segregation degree inside the grains. Microstructure evolution during solidification initiates from a primary nucleus firstly and then changed to a non-dendritic grain structure. The thermal analysis confirms the thermodynamic conditions for the formation of non-dendritic grain structure evolution.

Abstract: Silver nanocomposites are of great interest for several fields, ranging from packaging to biomedical applications, because of their known antibacterial properties. However, their use is strongly limited by technological issues: synthesis methods of silver nanoparticles are still difficult to control in terms of size, shape and aggregation. Moreover separation of nanoparticle aggregates should occur during part manufacturing by mixing with the polymer base but this process is also troublesome. In the present study, a new process to fabricate silver nanocomposites with antibacterial properties is presented. Silver nanofilms are deposited by radio frequency (RF) sputtering on polypropylene (PP) substrates. Consequently PP coated substrates are cut and inserted in a small-scale polymer mixer to produce the nanocomposite in a single step, without the need of producing nanoparticles. In fact, nanoparticles originate by the fragmentation of the nanocoating. Microscopic observations of nanocomposites revealed silver nanoclusters of different sizes. Their antibacterial activity has been verified in accordance to ISO 22196. The antibacterial activity of the nanocomposite was detected for the Escherichia coli and Staphylococcus aureus bacteria.

Abstract: The recrystallisation and precipitation kinetics of a plain carbon steel with 0.017 % Nb were studied using the double-hit deformation technique for interpass holding of 5 and 20s. The present study focuses on the effect of prestrain and deformation temperature on recrystallisation behaviour of the investigated steel. The fractional softening was calculated based on the percentage difference between the areas under the interrupted and uninterrupted deformations flow curves. The T_5% and T_95%, marking the beginning and end of recrystallisation, respectively, are determined as a function of strain. Quantitative microstructural studies validated the findings from the softening studies. The predicated results of recrystallisation regime are found to be in agreement with industrial observation and other experimental measurement for this steel. It can be seen that the dilute additions of Nb can influence the static recrystallisation of austenite under certain rolling condition which may lead to improved mechanical properties of steel.

Abstract: An area of major interest in biomedical engineering is currently the development of improved materials for medical implants. Research efforts are being focused on the investigation of surface modification methods for metallic prostheses due to the fundamental bioinert character of these materials and the possible ion release from their surfaces, which could potentially induce the interfacial loosening of devices after implantation. Electron beam (EB) structuring is a novel technique to control the surface topography in metals. Electrophoretic deposition (EPD) offers the feasibility to deposit at room temperature a variety of materials on conductive substrates from colloidal suspensions under electric fields. In this work single layers of chitosan composite coatings containing titania nanoparticles (n-TiO₂) were deposit by EPD on electron beam (EB) structured Ti6Al4V titanium alloy. Surface structures were designed following different criteria in order to develop specific topography on the Ti6Al4V substrate. n-TiO₂ particles were used as a model particle in order to demonstrate the versatility of the proposed technique for achieving homogenous chitosan based coatings on structured surfaces. A linear relation between EPD time and deposition yield on different patterned Ti6Al4V surfaces was determined under constant voltage conditions, obtaining homogeneous EPD coatings which replicate the 3D structure (pattern) of the substrate surface. The present results show that a combination of both techniques can be considered a promising surface modification approach for metallic implants, which should lead to improved interaction between the implant surface and the biological environment for orthopaedic applications.

Abstract: The development and application of low density alloys, such as Al and Mg alloys, has rapidly increased in the automotive sector in recent years. This necessitates advanced characterization techniques to assess the evolution of microstructure and phases during casting and processing. Further, understanding the mechanism of evolution of the defects is important in ensuring their minimization. Neutron diffraction has provided a method to determine the factors that trigger hot tearing in Al and Mg alloys as well as determining factors compromising integrity of powertrain components. In addition, neutron diffraction has been applied to examine the phase evolution during solidification of Al and Mg alloys enabling a better understanding of the effect of inoculants and solute additions on the solidification characteristics, resulting in improved castability. This paper highlights the frontiers of neutron diffraction analysis undertaken by the Centre for Near-Net-Shape Processing of Materials, Ryerson University and the CNL-Canadian Neutron Beam Centre.

Abstract: In the present study, we investigate the performance of efficient pair potentials in comparison to accurate ab initio potentials as energy descriptions for Monte Carlo simulations of solid-state precipitation. As test scenario, we take the phase decomposition kinetics in binary Fe_1-xCu_x. In a first effort, we predict thermodynamic equilibrium properties of bcc-rich Cu precipitates in an Fe-rich solution with a temperature and composition dependent Cluster Expansion. For this Cluster Expansion, combined ab inito and phonon calculations for various configurations serve as input. Alternatively, we apply the Local Chemical Environment approach, where the energy is described by computationally efficient pair potentials, which are calibrated on the first principles cluster expansion results. We observe that these fundamentally different approaches provide similar information in terms of the precipitate radius, chemical composition and interface constitution, however, the computational effort for the Local Chemical environment approach is significantly lower.

Abstract: Biomedical engineering is an advanced technology based on an extremely complex development of advanced biomaterials. Since the first Consensus Conference in Chester (UK) on Definitions in Biomaterials of the European Society for Biomaterials, in 1986, biomaterial was defined as ‘a bioinert or bioactive material used in a material advice, intended to interact with biological systems, restore functions of natural living tissues and organism in the body’. In this way, passive metallic materials (as titanium alloys), a broad spectrum of bioceramics, even biopolymers and all combinations of these biomaterials are used for numerous medical devices owing to their high biocompatibility. For example, titanium alloys can be employed for the femoral stems in the total hip joint replacement (trh) or for dental applications. Among the different clinical aims of an implant, a high osseointegration is required and crucial. In order to prevent the alloys from the aggressive body environment, surface modification of implants are employed to render them protection from both wear, corrosion and even tribocorrosion. In addition to the surface treatments, new implant materials are also being fabricated with biocompatible alloying elements to reduce the toxic effects of the alloying elements. These presentation describes the methodologies that could be adapted to overcome some of the factors leading to implant failure. It gives a panorama and shows that the different processes can increase noticeably the performance of the alloy as orthopedic and dental implant. It also gives prospects for the development of new possible ways for enhancing the biosecurity of such material.

Abstract: W is a plasma-facing material candidate for applications in future nuclear fusion reactors (NFR). In this work transient thermal loads of high energy have been simulated by interaction with a single laser pulse. The experiments have been carried out by using the Nd:Glass TVLPS laser working in first harmonic (wavelength λ = 1064 nm); the pulse parameters are: energy E ≈ 8 J, pulse duration ∆t ≈ 15 ns, focal spot size Φ = 200 μm, surface power density on the focal plane I = 1.7 x 10¹² W/cm².The damage produced by the laser pulse on the surface of bulk and plasma sprayed W has been investigated by Scanning Electron Microscopy (SEM) observations. The preliminary results will be presented.