1,721,106 research outputs found
Instrumented Nanoindentation Tests Applied to Bulk Metallic Materials: From Calibration Issue to Pile-Up Phenomena
Full text linkInstrumented nanoindentation tests have reached an effective level of theoretical and
practical knowledge to become an interesting and useful tool for determining hardness, H, and local
elasticity (reduced Young’s modulus), Er, of a variety of materials, from coatings and thin films
to bulk metallic materials. Nanoindentation instruments are equipped with analysis software for
raw data for hardness and reduced Young’s modulus evaluation, generally based on the Oliver
and Pharr analysis method. On the other hand, it is widely known and recognized that prior data
acquisition, a tip-dependent calibration procedure of compliance, and area function are needed. With
this in view, an accurate and sound calibration protocol is here reported. Hardness and local elastic
modulus is measured on different bulk metallic materials, showing the distinctive strengths of using
nanoindentation. Finally, a local elastic-plastic phenomenon mostly induced by the nanoindentation
tip on ductile metallic material (i.e., pile-up) is also reported and modelled. This manuscript is thus
intended to favor and account for the importance of using the instrumented nanoindentation tests
for H and Er measurements of metallic materials
Intermetallics as innovative CRM-free materials
Full text linkMany of currently used technical materials cannot be imagined without the use of critical raw materials. They require chromium (e.g. in stainless and tool steels), tungsten and cobalt (tool materials, heat resistant alloys), niobium (steels and modern biomaterials). Therefore there is a need to find substitutes to help the European economy. A promising solution can be the application of intermetallics. These materials offer wide variety of interesting properties, such as high hardness and wear resistance or high chemical resistance. In this paper, the overview of possible substitute materials among intermetallics is presented. Intermetallics based on aluminides and silicides are shown as corrosion resistant materials, composites composed of ceramics in intermetallic matrix as possible tool materials. The manufacturing processes are being developed to minimize the disadvantages of these materials, mainly the room-temperature brittleness
Effect of T5 and T6 heat treatments on cold deformation of a thixocast aluminium alloy
No full textEffect of T5 and T6 heat treatments on cold deformation of a thixocast aluminium alloy was investigated. A speroidisation of silicon particles and a redistribution of solute elements from the eutectic to the globule were observed on exposure to high temperatures. Hardness measurements revealed a delay in the precipitation process in T5 with respect to T6 due to lack of supersaturation. T5 aging treatments were found to give satisfactory results for elongation as the ductility values were comparable to that of T6. The results revealed better mechanical properties for the heat treated alloy in comparison to the alloy produced by other casting techniques
Creep response of Ti–6Al–4V alloy produced by additive manufacturing: Effect of annealing at 1050 °C
Full text linkThe present study mainly aims at investigating the creep response of a Ti-6Al-4V alloy produced by additive manufacturing and annealed above the 8-transus, and at rationalizing the differences observed when comparing its behaviour to that of the same alloy annealed at lower temperatures. Herein, the creep response of this alloy produced by additive manufacturing and subsequently annealed at 1050 degrees C is investigated at temperatures ranging from 500 to 650 degrees C. The heat treatment produces the typical Widmansta center dot tten microstructure with thin 8 -lamellae interposed between coarse a-lamellae. The minimum creep rate dependence on the applied stress and temperature is compared with literature data of tests of alloys with Widmansta center dot tten microstructures produced by traditional technologies. A modified form of an equation, successfully used to describe the creep responses of the Ti-6Al-4V alloy with different initial microstructures, was here proposed. The suggested modification introduces a threshold stress, which is related to the presence of finely spaced a-8 interfaces and a2-Ti3Al particles. This threshold stress is considered to be negligible when the distance between the a-8 interfaces is long and the a2-Ti3Al particles are absent or excessively spaced. In contrast, in the materials with Widmansta center dot tten microstruc- tures, even minor differences in the heat treatment conditions and/or the processing history cause considerable variations in the distance between the a-8 interfaces. This coupled with the occasional precipitation of a2-Ti3Al particles results in different threshold stress values
Mechanical spectroscopy study of as-cast and additive manufactured AlSi10Mg
Full text linkThe AlSi10Mg alloy produced by casting (AC) and additive manufacturing (AM) technology of laser powder bed fusion (L-PBF) has been investigated through mechanical spectroscopy (MS). In addition to the grain boundary peak PGB the Q−1 curves of both materials exhibit two other relaxation peaks, P1 (H = 0.8 ± 0.05 eV; τ0 = 10−11±1 s) and P2 (H = 1.0 ± 0.05 eV; τ0 = 10−13±1 s), depending on the interaction of dislocations with solute elements (Si and Mg). Relaxation strengths of P1, P2 and PGB of AM alloy are greater than those of the AC one owing to the finer structure of Al cells and the higher amount of Si and Mg in supersaturated solid solution induced by the rapid solidification typical of the L-PBF process. After successive MS test runs relaxation strengths of P1 and P2 peaks in both the examined materials decrease due to the precipitation of Si atoms and dislocation density recovery. Such decrease is more pronounced in AM alloy where change of cell shape and increase of cell size is observed. Dynamic modulus of AM alloy exhibits an anomalous trend in the first test run that is no more present in successive runs. The irreversible process giving rise to such anomalous behavior is the closure of pores of nanometric size
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Creep behaviour of a AlSiMg alloy produced by additive manufacturing
No full textThe present study aims at investigating the effect of the peculiar microstructure of additive manufactured samples on the creep behavior of a AlSiMg alloy. Constant load creep experiments were carried out between 150 and 205°C on an AlSiMg alloy produced by Powder Bed Fusion Additive Manufacturing (AM). The samples were mostly strained up to rupture, although in some cases the test were interrupted at the early onset of the tertiary region. Analyzing the time-to rupture, in the different load and temperature conditions, as a function of the applied stress, it can be clearly seen that the alloy produced by AM is substantially comparable, in terms of time to rupture, with an alloy of similar composition, tested in the die-cast state. The high values of the stress exponent suggest that the creep behavior is strongly affected by the presence of secondary-phase particles
On the creep performance of the Ti‐6Al‐4V alloy processed by additive manufacturing
Full text linkThe creep response of a Ti‐6Al‐4V alloy produced by additive manufacturing was investigated at 500, 600, and 650 °C using constant load experiments. A collection of recent data from the literature on Ti‐6Al‐4V produced by conventional technologies and heat treated to produce different microstructures was analysed to determine the effect of the microstructure on the creep behaviour of this material. A unique constitutive equation derived from a model developed for face-centred cubic (fcc) metals was successfully used to describe the creep response, irrespective of the different microstructures. The same constitutive model was able to provide an excellent description of the minimum creep rate dependence on the applied stress for the alloy produced by additive manufacturing, notwithstanding the obvious differences in the microstructures. These observations led to the reconsideration of some consolidated opinions on the behaviour of Ti‐6Al‐4V, shedding light on the substantial similarities in the creep responses when the microstructure has different morphologies. The initial microstructural features, which have traditionally been thought to greatly influence the creep response, indeed played an important role because they determined the magnitude of the ultimate tensile strength, but this effect gradually disappeared at high temperatures and low stresses
Static and dynamic precipitation phenomena in laser powder bed-fused Ti6Al4V alloy
Full text linkThe present paper investigates static and dynamic precipitation phenomena in the Ti6Al4V alloy produced via laser-powder bed fusion, solubilized at 1050 degrees C and aged in the range of 450-650 degrees C. In relation to the distance from the platform on which the samples are disposed during the solution heat treatment, the microstructure varies from alpha-laths to alpha-colonies arranged in a Widmanstatten structure. The aging heat treatment at 450 degrees C promotes the formation of stacking faults into alpha-laths and the precipitation of alpha(2)-Ti3Al phases. SEM and TEM observations reveal that the density of precipitates increases after aging at 500 degrees C, while coarsening of the alpha-phase occurs only after aging heat treatment at 600 degrees C. Vickers microhardness measurements reveal different peak-aging conditions and show that the alloy is unstable at high temperatures (T > 450 degrees C), both in the case of static and dynamic precipitation phenomena. Only the aging profile at 450 degrees C shows a constant trend of Vickers microhardness after 4 h of treatment
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