On the origin of the high tensile strength and ductility of additively manufactured 316L stainless steel: Multiscale investigation

We report that 316L austenitic stainless steel fabricated by direct laser deposition (DLD), an additive manufacturing (AM) process, have a higher yield strength than that of conventional 316L while keeping high ductility. More interestingly, no clear anisotropy in tensile properties was observed between the building and the scanning direction of the 3D printed steel. Metallographic examination of the as-built parts shows a heterogeneous solidification cellular microstructure. Transmission electron microscopy observations coupled with Energy Dispersive X-ray Spectrometry (EDS) reveal the presence of chemical micro-segregation correlated with high dislocation density at cell boundaries as well as the in-situ formation of well-dispersed oxides and transition-metal-rich precipitates. The hierarchical heterogeneous microstructure in the AM parts induces excellent strength of the 316L stainless steel while the low staking fault energy of the as-built 316L promotes the occurrence of abundant deformation twinning, in the origin of the high ductility of the AM steel. Without additional post-process treatments, the AM 316L proves that it can be used as a structural material or component for repair in mechanical construction

Stability of GPS and GLONASS onboard clocks on a monthly basis

This paper presents the stability of the GPS and GLONASS system clocks’ stability. It describes the construction of these two systems and calculated four different Allan variances (AVAR), based on the MGEX (the Multi-GNSS Experiment) clock products. Four used variances allowed making a better analysis of each GNSS system clock. The results are shown at different averaging times from 5 s as successive multiples to 655,360 s in a monthly period. The stability of GPS and GLONASS clocks is included in the range of 10-12~10-14 s. The results showed that GLONASS clocks are stable (10-12~10-14 s) and are affected with white frequency noise (WFM). The GPS clock stability models have more fluctuations for τ > 40,960 s and the mean stability is concluded between 10-12~10-13 s. Mean frequency accuracy for GPS clocks is related with WFM and Random Walk Frequency (RWF). The differences in clock stability are caused by several factors – block type, type of clock and the time of a satellite in orbit. These factors have an influence on stability results

Impact of selected parameters on the development of boiling and flow resistance in the minichannel

The paper presents results of flow boiling in a rectangular minichannel 1 mm deep, 40 mm wide and 360 mm long. The heating element for FC-72 flowing in the minichannel was the thin alloy foil designated as Haynes-230. There was a microstructure on the side of the foil which comes into contact with fluid in the channel. Two types of microstructured heating surfaces: one with micro-recesses distributed evenly and another with mini-recesses distributed unevenly were used. The paper compares the impact of the microstructured heating surface and minichannel positions on the development of boiling and two phase flow pressure drop. The local heat transfer coefficients and flow resistance obtained in experiment using three positions of the minichannel, e.g.: 0°, 90° and 180° were analyzed. The study of the selected thermal and flow parameters (mass flux density and inlet pressure), geometric parameters and type of cooling liquid on the boiling heat transfer was also conducted. The most important factor turned out to be channel orientation. Application of the enhanced heating surface caused the increase of the heat transfer coefficient from several to several tens per cent, in relation to the plain surface

Impact of selected parameters on the development of boiling and flow resistance in the minichannel

The paper presents results of flow boiling in a rectangular minichannel 1 mm deep, 40 mm wide and 360 mm long. The heating element for FC-72 flowing in the minichannel was the thin alloy foil designated as Haynes-230. There was a microstructure on the side of the foil which comes into contact with fluid in the channel. Two types of microstructured heating surfaces: one with micro-recesses distributed evenly and another with mini-recesses distributed unevenly were used. The paper compares the impact of the microstructured heating surface and minichannel positions on the development of boiling and two phase flow pressure drop. The local heat transfer coefficients and flow resistance obtained in experiment using three positions of the minichannel, e.g.: 0°, 90° and 180° were analyzed. The study of the selected thermal and flow parameters (mass flux density and inlet pressure), geometric parameters and type of cooling liquid on the boiling heat transfer was also conducted. The most important factor turned out to be channel orientation. Application of the enhanced heating surface caused the increase of the heat transfer coefficient from several to several tens per cent, in relation to the plain surface

The Structure of FeAl Sinters Fabricated Using Cyclic Loading

A two stage process including a sintering under a cyclic loading is proposed as an alternative fabrication method of dense FeAl intermetallics from elemental powder mixtures. The first stage (pre-sintering) is conducted at two temperature values (620 °C and 670 °C, respectively) under a static and a cyclic loading with a frequency of 20, 40 and 60 Hz. The second one includes a pressureless sintering at temperature of 1250 °C, under a protective argon atmosphere. A suitable selection of pre-sintering parameters (temperature, type and frequency of pressing) allows approximately five times grain size reduction of FeAl phase in comparison to particle size of raw Fe and Al powder material (40–60 µm), as well as induces an effective fragmentation of oxide layers. For the sinters obtained using 60 Hz loading frequency an oxide particle size of 4.0 or 4.5 µm (smaller for sintering with liquid phase) is observed. Material obtained after the full heat treatment are characterized by a fine-grained structure of chemically homogeneous FeAl phase with uniformly distributed Al2O3 spherical particles along grain boundaries. Moreover, it was found that temperature and frequency of loading during the presintering process also affect a consolidation level of the Fe-Al powder mixture, which increases with rising both temperature and frequency

Obróbka elektroerozyjna spieków na osnowie fazy międzymetalicznej feal bez i z dodatkiem nanoceramiki Al2O3

The influence of the parameters of wire electrical discharge machining (WEDM) on the surface layer of FeAl based sinters with and without Al2O3 nanoceramic addition has been studied in this paper. The properties of the sinters surface layer were controlled by WEDM parameters, including time of interval (tp) and amplitude of current (IA). The WEDM roughing and finishing treatments were carried out for selected technological parameters of process. The surface texture (ST) of the sinters after WEDM was analyzed by profilometer method. Theoretical parameters describing abrasive wear resistance of investigated sinters were estimated on the basis on the load capacity curve. On the basis on obtained results it can be stated that there is possibility of shaping geometry of nano- Al2O3 doped and undoped FeAl sinters by WEDM. Reduction of the time of interval (t p) and increase of current amplitude (IA) during WEDM deteriorate surface properties. Addition of nano- Al2O3 improve the quality of the obtained surface. Applied parameters of WEDM improve theoretical abrasive wear resistance and lubricant maintenance of the nanoceramic doped material in comparison with undoped sinter.W niniejszej pracy analizowano wpływ parametrów cięcia elektrozyjnego (ang. WEDM – wire electrical discharge machining) na warstwę wierzchnią spieków na osnowie fazy międzymetalicznej FeAl bez i z dodatkiem nanoceremiki Al2O3. Poprzez zmianę parametrów obróbki elektroerozyjnej, tj. czas przerwy (tp) i natężenie prądu (IA), sterowano właściwościami warstwy wierzchniej obrabianych spieków. Dla wybranych parametrów technologicznych procesu przeprowadzono obróbkę zgrubną i wykańczającą. Strukturę geometryczną powierzchni (SGP) spieków po obróbce elektroerozyjnej analizowano za pomocą metody profilometrycznej. Parametry charakteryzujące teoretyczną odporność na zużycie ścierne zostały oszacowane na podstawie krzywych nośności Abbotta-Firestone’a. Na podstawie uzyskanych wyników stwierdzono, że istnieje możliwość kształtowania geometrii spieków FeAl bez i z dodatkiem nanoceramiki Al2O3 za pomocą obróbki elektroerozyjnej WEDM. Wraz ze skróceniem czasu przerwy i wzrostem natężenia prądu podczas obróbki wzrasta chropowatość obrabianych powierzchni, natomiast dodatek nanoceramiki poprawia jakość otrzymanych powierzchni. Zastosowane parametry obróbki WEDM poprawiły teoretyczną odporność na zużycie ścierne i zdolność do przechowywania środka smarnego powierzchni spieków domieszkowanych nanoceramiką, w porównaniu do materiału niedomieszkowanego

Comparison of the Microstructural, Mechanical and Corrosion Resistance Properties of Ti6Al4V Samples Manufactured by LENS and Subjected to Various Heat Treatments

In this paper, the influences of two post-heat treatments on the structural, mechanical and corrosion resistance properties of additively manufactured Ti6Al4V alloys were discussed in detail. The materials were produced using the laser engineering net shaping (LENS) technique, and they were subjected to annealing without pressure and hot isostatic pressing (HIP) under a pressure of 300 MPa for 30 min at temperatures of 950 °C and 1050 °C. Annealing without pressure led to the formation of a thin plate structure, which was accompanied by decreasing mechanical properties and increasing elongation and corrosion resistance values. For the HIP process, the formation of a thick plate structure could be observed, resulting in the material exhibiting optimal mechanical properties and unusually high elongation. The best mechanical and corrosion resistance properties were obtained for the material subjected to HIP at 950 °C