Materials Science Forum Vol. 1016

Abstract: The ferroelectric solid solutions described by a general formula 0.98Pb(Zr_1-xTi_x)O₃ – 0.02La(Fe³⁺_0.5, Nb⁵⁺_0.5)O₃ have been obtained by solid state reaction technique, where x assumes the following values: 0.42, 0.48 and 0.58. The structure of these ferroelectric compositions has been investigated in detail using X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). The results obtained by XRD have evidenced that all obtained samples have a perovskite structure. The influence of the sintering temperature on the degree of incorporation of the elements in the solid solution have been studied too. The dielectric and piezoelectric constants have been determined and the influence of temperature on obtained values are presented and discussed. The performed experimental results have pointed out that the materials are characterized by a high anisotropy. Furthermore, the obtained values of the electromechanical coupling factor (k_p) is situated between 0.40÷0.65 depending on the composition and the sintering temperature too.

Abstract: Industrial-scale extruded profiles of AA 7108 with a rectangular section (25.60 mm x 15.95 mm) were used in this investigation. Some complementary microstructural analysis techniques, such as polarized light microscopy, EBSD (Electron Backscatter Diffraction) and X-ray diffraction were used to characterize the microstructure, focusing on the PCG zone. It was observed that the extruded profiles presented a totally recrystallized microstructure and a 300 μm layer of peripheral coarse grains. Additionally, the results showed that the PCGZ predominant grain orientation {311} <110> differs from the texture below the PCGZ (Goss and Cube components).

Abstract: The main objective of the present work was to characterize the phases that are present after solution annealing in the microstructure of the titanium stabilized austenitic stainless steel W.-Nr. 1.4970, developed as a candidate material for fast breeder reactor fuel cladding. The crystalline structure, chemical composition, quantity, size, morphology, and distribution of the phases present in the microstructure after solution annealing heat treatments were studied in detail with the help of several complementary techniques. Chemical dissolution of the matrix has been performed using the Berzelius solution and the extracted residue has been analyzed by X-ray diffraction in a high precision camera. Three phases have been observed and identified after solution annealing heat treatments performed in the 1090 to 1300 °C temperature range, namely: (Ti,Mo)C; Ti (N,C) and Ti₄C₂S₂. The Ti-nitride and the Ti-carbosulfide did not dissolve in the steel matrix up to 1300 °C, on the other hand, the solubility of the (Ti,Mo)C raised strongly with temperature. A solution annealing heat treatment is recommended for the W. Nr. 1.4970 stainless steel.

Abstract: We have determined different phase fractions from microscopy images using semi-automated image analysis fitting technique, and in addition we have classified each phase according to its hardness. The distribution of grayscale pixels of different phases is first characterised separately for each phase, which are sampled from the microscope image. After this the distributions of the separate phases are fitted to give the corresponding distribution of the whole image. The microhardness measurement provides reliability on the classification of the different phases to ferrite, bainite or martensite. In addition to describing the applied techniques in detail, we present the results obtained from the analysis for one steel subjected to isothermal holding experiments at different temperatures.

Abstract: Either at higher temperatures or when a certain alloying element content is exceeded, γ-TiAl alloys contain the β phase (bcc) or its ordered derivate β_o (B2). The relatively soft β phase can facilitate hot deformation, but β_o is detrimental for creep strength and ductility. Thus, knowledge about β_o→β phase transformation is desirable. Surprisingly, even for the binary Ti-Al system it is under discussion whether the ordered β_o phase exists. Also, the effect of alloying elements on the β phase ordering is still unclear. In the present work the ordering of the β phase in binary Ti-(39,42,45)Al and ternary Ti-42Al-2X alloys (X=Fe, Cr, Nb, Ta, Mo) which was experimentally investigated by neutron and high energy X-ray diffraction is compared with the results of first principles calculations using density functional theory. Except for Cr the experimentally determined and the predicted behavior correspond.

Abstract: The plasma spraying is commonly used in medical application. The Atmospheric Plasma Spray (APS) method was applied for production of yttria-stabilized zirconia (YSZ) on AISI 316L stainless steel surface and also on Ti6Al4V titanium alloy surface. In present article two examples of coatings production were presented. In first experimental the YSZ was plasma sprayed (APS) on 316L stainless steel surface. The coating was deposited using A60 (Thermico) plasma torch. The initial parameters were selected and it was concluded that minimal power current was 500A. The thickness of obtained coating was in range 100-150 micrometers. The X-ray phase analysis showed the presence of tetragonal t-phase of ZrO₂. The lamellar structure of coatings with large porosity was observed. In second experimental the newly developed Plasma Spray Physical Vapor Deposition method (PS-PVD) was used. The YSZ coating was deposited on titanium Grade 5 surface. The conducted research showed the formation of two types of coatings structure. When the power current was lower (2000 A) the dense lamellar-like coatings was obtained. If the power current was increased (up to 2200A) the columnar ceramic coating was observed.

Abstract: In the present study, microstructural and crystallographic features of an Al-Fe binary alloy with a near eutectic composition (Al-2.5wt%Fe) fabricated by laser powder bed fusion (LPBF) process were examined. The LPBF processing for the Al-Fe alloy powder was conducted at room temperature using a 3D Systems ProX 200 operating at a laser power of 204 W and a laser scan speed of 0.6 m/s and 0.8 m/s to fabricate cube samples with high relative density above 99 %. The fabricated sample exhibited characteristic microstructure consisting of a number of melt pools in which the regions had locally melted and rapidly solidified by laser irradiation during the LPBF process. Numerous fine particles of Al-Fe intermetallics with a mean size below 100 nm were found within the α-Al matrix in the observed melt pools, whereas relatively coarsened particles were localized around melt pool boundaries. Electron backscatter diffraction (EBSD) analyses revealed a number of columnar a-Al grains with a mean size of approximately 10 μm. The LPBF-fabricated Al-Fe alloy exhibits a high hardness of approximately 90 HV, which is more than twice higher than the conventionally casted Al-Fe alloy.

Abstract: Effects of extrusion temperature and heat treatment process on the microstructure and mechanical properties of Ti-1300 titanium alloy tube billets were studied by tensile testing and microstructure observation, and the relationship among the thermal processing technique and microscopic structure and mechanical properties of the billets were also investigated. The results showed that the transverse structure of Ti-1300 alloy after extrusion in the a+b two-phase region was uniform and fine. And the longitudinal structure could be seen that the extrusion processing streamline was broken uniformly. Ti-1300 alloy extruded at a+b two-phase has a good match of the strength and ductility, and the ductility of two-phase extrusion is obviously better than that of β single-phase extrusion, especially for the reduction of area.

Abstract: In this paper, we report a lamellar-structured low-alloy transformation-induced plasticity (TRIP) steel; the microstructure of the steel consists of alternate lamellae of intercritical ferrite and reverted austenite on microscale, with the latter consisting of bainitic ferrite laths and retained austenite films on nanoscale. Such a microstructure was produced by a heat treatment process similar to that for producing conventional TRIP-assisted steels, i.e. intercritical annealing followed by austempering. Nevertheless, quenched martensite rather than a mixture of ferrite and pearlite was used as the starting structure for intercritical annealing to form austenite, and the resulting austenite was then transformed to bainite by austempering treatment. This steel exhibits much enhanced strength-ductility combinations as compared with those conventional polygonal-structured low-alloy TRIP steels.

Abstract: Fatigue crack growth resistance of ultrafine grained Cu processed by equal channel angular pressing (ECAP) was investigated. Particular emphasis was devoted to the effects of microstructure evolution on fatigue crack growth in the near-threshold regime. The ultrafine grained Cu exhibits a lower fatigue threshold than coarse-grained Cu at stress ratios of 0.1 and 0.7. Fatigue induced coarsening of the UFG structure near the fatigue crack and intergranular fatigue crack growth are observed.