Directed Energy Deposition of Low-Alloyed Steels: An Insight on Microstructural and Mechanical Properties

Low-alloyed steels are used for a variety of different applications like bearings or gears. Additive manufacturing technologies like directed energy deposition (DED-LB/M) allow for a fast and close-to-contour fabrication of sophisticated products without excessive waste of material. However, the DED-LB/M process cannot be considered as state-of-the-art for this group of materials. This study presents findings on the material properties of the additively manufactured low-alloyed steel Bainidur AM by means of DED-LB/M. This includes studies on the mechanical properties (hardness, compression strength) as well as the microstructural properties (scanning electron microscopy [SEM]). The microstructure in the as-built state appears like a bainitic–martensitic one with shares of retained austenite which is not fully transformed during cooling. As a differentiation is barely possible from the SEM images, a plethora of investigations is further used to assess the microstructure. As-built samples possess a good combination of ductility and hardness. Furthermore, the specimens are characterized by a good tempering stability up to 600 °C. This tempering stability is characterized by a homogeneous hardness of around 400 HV1 for all temperatures. In contrast, the conventionally hardened specimens show a drop-off in material hardness, further indicating the excellent material properties of additively manufactured Bainidur AM.     

High-Entropy Alloy-Induced Metallic Glass Transformation: Challenges Posed by in situ Alloying via Additive Manufacturing

In situ alloying and fabricating glassy structures through a layer-by-layer fashion approach are challenging but have high potential to develop novel-graded materials. For the first time, this cost-effective approach is applied to additive manufacturing (AM) of a Zr-based bulk metallic glass (BMG) from high-entropy alloys (HEAs). A newly developed composition of Zr₄₀Al₂₀Cu₂₀Ti₂₀ is fabricated through laser powder bed fusion (LPBF). Process parameters are optimized within a wide range of laser power (50–200 W) as well as scanning speed (50–800 mm s⁻¹). In all printed samples, microscopic and compositional examinations reveal no glass formation, but very fine grains and CuTi and AlTi nanocrystals. Some glassy transitions at the interfaces may be encouraged to occur with proper melting and mixing. However, the main reason for not obtaining a glassy matrix is the substantial proportion of unmelted Zr raw powder throughout the structure as spherical particles. Consequently, glass formation can be hindered by a considerable amount of compositional deviation. During LPBF, in situ alloying poses significant challenges to developing BMGs. Hence, the various stages of the process, including raw material specifications, laser settings, and process parameters, should be investigated further.     

Effect of the line scanning driving of active-matrix display on the measurement of display temporal characteristics

Temporal characteristics are crucial factors influencing display performance. For an active-matrix display, signals are applied sequentially line-by-line, and the temporal response of each horizontal line changes depending on different timings. When recording the temporal response of a display, the probe of the measuring device must have the finite size and shutter time. As the finite-size probe records the temporal responses of multiple lines with different timings, the number of lines covered by the finite-size probe affects the obtained result. And the effects due to the timing difference of the sequential driving can be misinterpreted as the temporal response of the display. In this study, the contribution of the various factors, such as the camera shutter time, probe size of the measuring device, temporal transition time, and display frame rate was evaluated to separate the temporal characteristics of the display from the effect caused by these factors. A procedure to estimate only the temporal response of a display without such effects is devised. The effectiveness of the proposed procedure was verified based on the spatial temporal record obtained by a high-speed camera of video frame rates of 9000 and 12,000 per second.     

Controlling properties of ceramic formulations for porcelain robocasting

Porcelain pastes (PlotPastes) were formulated to be used on an additive manufacturing (AM) process (material extrusion) process, primarily robocasting (R3D) technique. The material morphological and thermal characteristics were evaluated by scanning electron microscopy (SEM), differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The rheology and the electrical potential of the ceramic particles were also studied to select and adequate the porcelain paste properties to the R3D AM technique. It was found that shifting the pH values to acidic, the surface charge of the particles changes and increases the pastes viscosity due to agglomeration effects. This behaviour was exploited to optimize the paste rheological behaviour which resulted in the optimum pH at 1.94 (PlotPaste 5). This paste was used in the study of R3D operating parameters. It was found that small variations in pressure and speed affects the dimensional accuracy of the printed models. The results showed the disruptive potential of porcelain R3D in the production of customized ceramic products.     

Physicochemical properties of sweetpotato starch

Sweetpotato starch is high‐yielding, but has limited development and uses. In this study, physicochemical properties of sweetpotato starch from 11 representative genotypes with diverse geographic origins in China were characterized and showed wide variations. Apparent amylose contents measured by iodine binding ranged from 23.3 to 26.5%, by gel permeation chromatography after debranching from 17.5 to 23.9%, and true amylose content by concanavalin A binding from 15.9 to 22.5%. In vitro digestibility varied from 29.5 to 41.2%. Swelling power and water solubility index were highly correlated (r² = 0.88). Gelatinization peak temperature and enthalpy ranged from 75.4 to 79.7°C, and 7.6 to 13.6 J/g, respectively. Pasting peak and cold paste viscosities varied from 268 to 469 RVU, and 170 to 284 RVU. Amylose contents were highly correlated to digestibility, pasting, and thermal parameters.     

AA/AM/AMPS超浓反相乳液聚合合成钻井液降滤失剂的研究

所合成的AA／AM／AMPS三元共聚合超浓反相乳液以白油为外相，可直接用作水基钻井液的降滤失剂。根据2．0％反相孔液在淡水基浆中的降滤失效果，得到了最佳合成条件：单体在水相中的质量分数55％。水相体积分数85％，乳化剂为油相质量的12％，引发剂K2S2O8与单体的摩尔比为0.2％，单体中水化基团（羧酸根，磺酸根）与吸附基团（酰胺基）摩尔比为1：1，实验中为0．75：1。在淡水、盐水、饱和盐水、复合盐水基浆中加入2．0％反相乳液，其API滤失量分别为12.2、14.3、19.5、14.0mL，在150℃滚动老化16小时后分别为13．8、19．2、28．0、16．3mL。该反相乳液稳定性良好，在3000r／min离心分离60min，油相分离率为2．2％，在室温储存3个月。油相分离率为6．0％。图6表1参17。     

Non-oxide CMC fabricated by Fused Filament Fabrication (FFF)

The present study introduces an approach to additively manufacture non-oxidic Ceramic Matrix Composites (CMCs) by the Material Extrusion (MEX)-based Fused Filament Fabrication. Therefore, highly SiC particle filled thermoplastic filaments were developed containing short fibers and/or long fibers to maintain shape during the thermal treatment and exhibiting flaw tolerant behavior. Polymer Infiltration and Pyrolysis (PIP) was applied to densify the microstructure. It is shown that a low content of long fibers of about 5 % can already exhibit damage tolerance comparable to steel reinforced concrete. Thus, the mechanical behavior is different to conventional fiber composites with significant higher fiber volume content. Nevertheless, these results enable new opportunities for producing advanced complex CMC components by means of Additive Manufacturing (AM).     

HP（DMDAAC／AM）对MMA－膨润土泥浆体系的稀释作用

研究了二甲基二烯丙基氯化铵－丙烯酰胺共聚物的水解产物ＨＰ（ＤＭＤＡＡＣ／ＡＭ）对混合金属层状氢氧化物ＭＭＨ－膨润土泥浆体系的稀释作用。通过电性、流变性、滤失性、抑制性及粒度分布的研究，发现ＨＰ（ＤＭＤＡＡＣ／ＡＭ）对ＭＭＡ－膨润土泥浆有较强的稀释能力和一定的降失水作用；含ＨＰ（ＤＭＤＡＡＣ／ＡＭ）的ＭＭＡ－膨润土泥浆对粘土膨胀有很好的抑制性。ＨＰ（ＤＭＤＡＡＣ／ＡＭ）分子在粘土颗粒表面产生多点静电强吸附，破坏了ＭＭＨ与粘土颗粒形成的网状结构．释放出自由水，从而达到稀释效果。