The Effect of Seven Etching Solutions used for the Differentiated Visualization of Complex Microstructures in Low-Alloyed Cast Iron

For numerous steel grades, detailed descriptions of different etching techniques and etching times for microstructural analysis are available. However, there are only few reference works for low-alloyed cast iron. Particularly for complex microstructures with combined fractions of bainite, ferrite, pearlite, retained austenite, carbides and martensite, there are only few detailed collections. In addition, the effects of the etchants are rarely investigated for the same image section. Therefore, this study will exclusively compare identical microstructural regions and the effect of different etchants on them. Two specific sample areas were selected in a low-alloyed cast iron and the effect of both surface removal etching and tint etching reagents on them was examined under a reflected light optical microscope and a scanning electron microscope. The results of the study have shown that some etchants for complex microstructures are only suitable in case potentially present phases are already known. However, the combined use of two etching solutions in particular, led to a very detailed and highcontrast image, capable of revealing and resolving microstructures with a variety of phases.

Crystallization Behavior and Mechanical Properties of Poly(ε-caprolactone) Reinforced with Barium Sulfate Submicron Particles

Poly(ε-caprolactone) (PCL) was mixed with submicron particles of barium sulfate to obtain biodegradable radiopaque composites. X-ray images comparing with aluminum samples show that 15 wt.% barium sulfate (BaSO4) is sufficient to present radiopacity. Thermal studies by differential scanning calorimetry (DSC) show a statistically significant increase in PCL degree of crystallinity from 46% to 52% for 25 wt.% BaSO4. Non-isothermal crystallization tests were performed at different cooling rates to evaluate crystallization kinetics. The nucleation effect of BaSO4 was found to change the morphology and quantity of the primary crystals of PCL, which was also corroborated by the use of a polarized light optical microscope (PLOM). These results fit well with Avrami–Ozawa–Jeziorny model and show a secondary crystallization that contributes to an increase in crystal fraction with internal structure reorganization. The addition of barium sulfate particles in composite formulations with PCL improves stiffness but not strength for all compositions due to possible cavitation effects induced by debonding of reinforcement interphase.

Effect of strain ratio on hydrogen permeability properties of low carbon enamel steel

In this study, the effect of varying strain levels on hydrogen permeability properties were investigated. Distinct strain levels (10% and 40%) were carried out on the deep drawing test samples by using Marciniak die to simulate the forming process. Amount of strain on deep drawn material was calculated by GOM’s ARAMIS 3D deformation measurement system. Hydrogen diffusion coefficient and permeation time were calculated by using Helios II system. Light optical microscope (LOM) and scanning electron microscopy (SEM) were used for microstructure characterization. Automated inclusion/precipitation analysis was performed by Thermoscientific Explorer-4. By this study, it is aimed to understand the hydrogen permeation properties of ultra-low carbon IF steel material with varying strain values. Finally, it was determined that number of inclusion/precipitation per mm2 was significantly increased as a function of strain ratio, which improves hydrogen permeation properties.

Evaluation of microstructure of the steels after exposure in supercritical CO2

The Brayton cycle with supercritical carbon dioxide is considered as an innovative technology with the potential to replace conventional steam cycles. The optimization of the supercritical CO2 cycle (sCO2) is necessary and important to achieve the required thermal cycle parameters. The above optimization focuses on the setting of the energy cycle as such, the design solution of the individual components and, the last but not least, on the selection of suitable construction materials. Due to the operating conditions, namely temperatures exceeding 550 °C and pressure up to 25 MPa, material research is one of the important areas of the research and development of sCO2 energy cycles. Construction materials for sCO2 power cycle equipment include HR6W, T92 and Haynes HR235 alloys. This work presents results of the corrosion test, in which samples of these materials were exposed to sCO2 at 550 °C and 25 MPa for 1000 hours. Corrosion after exposure was examined using a light optical microscope (LOM) and a scanning electron microscope (SEM). The significant differences in corrosion attack between the investigated materials and the formation of a protective oxide layer on the surface were observed.

Effect of silicon on creep properties of titanium 6Al-2Sn-4Zr-2Mo alloy

The alloy Ti-6Al-2Sn-4Zr-2Mo is a titanium alloy for elevated temperatures often used in aerospace applications. Minor additions of silicon have proven to improve the creep resistance of this alloy. In this work, three different amounts of silicon (0.015, 0.07 and 0.162 wt% Si) were added to cast Ti-6242 and creep tests were performed at different temperatures and loads. Creep resistance increased significantly with silicon addition by means of silicide precipitation hindering dislocations movement. Silicon rich nanoparticles in the microstructure were detected and their effect on creep resistance was investigated. The instruments used in this study were light optical microscope (LOM) and scanning electron microscopy (SEM). Precipitates larger than 150 nm were found to be located heterogeneously in the microstructure, whereas smaller precipitates, ranging from 20-100 nm were homogeneously spread in the material. All silicides were predominantly situated next to the beta-phase in the alloy, either at the prior-beta grain boundaries or the beta-phase in between the alpha-colonies.

Laser Additive Manufacturing of Titanium Aluminides for Turbomachinery Applications

The defect-free processing of TiAl alloy TNM™-B1 by means of Laser Powder Bed Fusion (LPBF) is demonstrated by manufacturing of an automobile turbocharger wheel. Similar precision cast material was used as reference. TNM™-B1 was manufactured crack free with a density > 99.5% using elevated process temperatures above the brittle-to-ductile transient temperature (BDTT). The preheating temperature was provided by an induction preheating system. To minimize oxygen pick up during the LPBF process, the process atmosphere was actively cleaned using a gas-purification system. Produced test samples were analyzed in as-built and heat-treated condition regarding density, micro structure and phases by means of a Light Optical Microscope (LOM) and Scanning Electron Microscopy (SEM). Micro hardness was measured according to Vickers. Oxidation measurements were performed by means of carrier-gas hot extraction. Mechanical properties were determined using room temperature tensile tests. The final automobile turbocharger wheel was analyzed for defects using a Micro-Computer Tomography scanner (MCT). Besides bulk test samples, thin-walled specimens can be manufactured with sufficient density. Depending on the process parameters, an oxygen content < 1000 ppm could be reached. The as-built microstructure consists of lamellar (α2+γ) colonies and nearly globular γ as well as β/β0 at the grain boundaries. High cooling rates in the magnitude of 105 to 106 K/s provide small grain sizes of 1–7 μm. Hardness measurements reveal an increased hardness (515-560HV0.3) compared to cast material (390HV0.3). Samples for tensile tests show tensile strength around 840 MPa and a total elongation of 1.1% for LPBF-manufactured and hot isostatic pressed (HIP) samples. The CT analysis of the turbocharger wheel confirms that complex geometries made of TiAl can be additively manufactured free of cracks.

Experimental Determinations of Mixing Times in the IronArc Pilot Plant Process

IronArc is a newly developed technology and an emerging future process for pig iron production. The long-term goal with this technology is to reduce the CO2 emissions and energy consumption compared to existing technologies. The production rate of this process is dependent on the stirring, which was investigated in the pilot plant process by measuring the mixing time in the slag bath. Moreover, slag investigations were done both based on light optical microscope studies as well as by Thermo-Calc calculations in order to determine the phases of the slag during operation. This was done because the viscosity (which is another important parameter) is dependent on the liquid and solid fractions of the slag. The overall results show that it was possible to determine the mixing time by means of the addition of a tracer (MnO2 powder) to the slag. The mixing time for the trials showed that the slag was homogenized after seconds. For two of the trials, homogenization had already been reached in the second sample after tracer addition, which means ≤8 s. The phase analysis from the slag indicated that the slag is in a liquid state during the operation of the process.

Changes of the Magnetic Properties during Heat Treatment in AISI 304

The aim of this study was to evaluate changes of the magnetic properties during heat treatment in austenitic stainless steel AISI 304. Investigated changes were caused by plastic deformation in material. Specific composition of alloying elements in austenitic stainless steels has got influence on their deformation behavior. Samples were heat treated before measurement of magnetic properties in different intervals of temperatures. The first series of measurements has shown, that it is necessary to make more precise analysis of temperature intervals in the second part of experiment. For verification of structural changes in material there was used hardness test Vickers method and observation by light optical microscope. There was proven that AISI 304 is slightly magnetic after cold forming, although in general it is considered as non-magnetic.

Microstructure and Mechanical Characterization of X70 Steel Welded Joints Through Hardness Mapping and Tensile Strength Testing

In this paper, effects of preheating and type of electrode (E8010 and E8018) on microstructure and mechanical properties of 5L X70 steel welded joints were investigated. The microstructure of joint zone and fracture surface was analyzed by light optical microscope and scanning electron microscope equipped with energy dispersive spectroscopy. Hardness mapping and tensile test were also performed to find the relationship between microstructure and mechanical properties. The results showed a consistency between the hardness variation data and the microstructure of joint zone. Moreover, hardness mapping revealed coarse and fine grain subregions in the heat affected zone which were not detected in the micrographs. The tensile test indicated that the non-preheated sample, welded by cellulosic E8010, had the minimum value in the strength and the ductility of welded steel. The fractography also determined that size and distribution of strengthening phases affected the fracture mode of welded specimens.

Metal Injection Moulding of Ti-6Al-4V with Yttrium Addition

For highly loaded parts, such as medical implants as well as for engineering application, high strength and good ductility are indispensable, but also the fatigue resistance plays an important role. For both, quasi static and fatigue properties, a fine microstructure is essential. Furthermore, especially for titanium alloys the control of interstitial impurities like oxygen and nitrogen is very important. In a former study additions of several oxides of rare earth elements were tested with respect to their effect on the microstructure of MIM processed Ti-6Al-4V. Yttrium oxide has shown the strongest effect on the colony size of Ti-6Al-4V.In this study elementary yttrium powder was added to Ti-6Al-4V. During sintering, the yttrium scavenges oxygen out of the titanium matrix, increasing the ductility. The yttrium oxide, which is formed, leads to a colony refinement and therefore to a higher strength.For preliminary tests cylindrical samples consisting of Ti-6Al-4V powder blended with coarse yttrium powder and a wax and polyethylene-based binder were manufactured by uniaxial pressing and sintering. The addition of yttrium led to a slight decrease of the colony size: specimens sintered at a high temperature of 1400 °C show a stronger dependency of yttrium content on the colony size than those sintered at 1300 °C.Tensile test specimens were produced by MIM using gas atomized Ti-6Al-4V-powder with additions of yttrium powder between 0.1 and 0.5 wt.-%. Sintering took place at temperatures between 1300 °C and 1400 °C with two different dwell times (2 and 4 hours). Tensile tests were conducted in air at room temperature. The microstructures were observed by SEM and light optical microscope. Oxygen and nitrogen contents were analysed by a melt extraction technique.