The paper presents results of a study concerning an AlSi7Mg alloy and the effect of subjecting the liquid metal to four different processes: conventional refining with hexachloroethane; the same refining followed by modification with titanium, boron, and sodium; refining by purging with argon carried out in parallel with modification with titanium and boron salts and strontium; and parallel refining with argon and modification with titanium, boron, and sodium salts. The effect of these four processes on compactness of the material, parameters of microstructure, and fatigue strength of AlSi7Mg alloy after heat treatment. It has been found that the highest compactness (the lowest porosity ratio value) and the most favorable values of the examined parameters of microstructure were demonstrated by the alloy obtained with the use of the process including parallel purging with argon and modification with salts of titanium, boron, and sodium. It has been found that in the fatigue cracking process observed in all the four variants of the liquid metal treatment, the crucial role in initiation of fatigue cracks was played by porosity. Application of the process consisting in refining by purging with argon parallel to modification with Ti, B, and Na salts allowed to refine the microstructure and reduce significantly porosity of the alloy extending thus the time of initiation and propagation of fatigue cracks. The ultimate effect consisted in a distinct increase of the fatigue limit value.
This article presents a study of the crystallization and microstructure of the AlSi9 alloy (EN AC-AlSi9) used for the alfin processing of iron ring supports in castings of silumin pistons. Alfin processing in brief is based on submerging an iron casting in an Al-Si bath, maintaining it there for a defined time period, placing it in a chill mould casting machine and immersing it in the alloy. This technology is used for iron ring supports in the pistons of internal combustion engines, among others. Thermal analysis shows that when the AlSi9 alloy contains a minimal content of iron, nucleation and increase in the triple (Al)+Fe+(Si) eutectic containing the -Al8Fe2Si phase takes place at the end of the crystallization of the double (Al)+(Si) eutectic. Due to the morphology of the ”Chinese script” the -Al8Fe2Si phase is beneficial and does not reduce the alloy’s brittleness. After approx. 5 hours of alfin processing, the -Al5FeSi phase crystallizes as a component of the +Al5FeSi+(Si) eutectic. Its disadvantageous morphology is ”platelike” with sharp corners, and in a microsection of the surface, ”needles” with pointed corners are visible, with increases the fragility of the AlSi9 alloys.
The text discusses the problems of sensory processing disorders (SPD) and their impact on difficulties children have at school. Individual categories of sensory processing disorders were characterized and examples of behavior of children who may have those problems were described. Certain strategies which teachers can use when working with a child with SI disorders were also offered.
It should be noted that the early diagnosis of symptoms that may indicate the occurrence of sensory processing disorders, followed by apt diagnosis and therapy allow children to function properly in the school environment and positively influence their self-esteem. This in turn facilitates the process of learning and contributes future success.
Copper have always been an important material and incorporation of elements into copper for property enhancement. Bronze is a relevant cuprous alloy which is important for many industrial and automotive applications like bearings and machineries. The present research is directed towards the fabrication and tribological analysis of regular bronze (Cu-6Sn) and metal matrix composites reinforced with varying particle sized SiC ceramic reinforcement (30, 35 and 40 μm). The developed specimens were subjected to wear analysis according to ASTM standards, to identify the tribological properties utilizing a pin on disk tribometer. It was noted that the wear rates of developed MMC’s phenomenally decremented with an increase in size of SiC particle reinforcement. Also, the test parameters were influential in altering the wear rates to notable margins. The standard scanning electron microscopy techniques aided in identifying the influence of adhesive wear on the specimen surface.
Monitoring the solidification process is of great importance for understanding the quality of the melt, for controlling it, and for predicting the true properties of the alloy. Solidification is accompanied by the development of heat, the magnitude of which depends on the different phases occurring during solidification. Thermal analysis is now an important part of and tool for quality control, especially when using secondary aluminium alloys in the automotive industry. The effect of remelting on the change of crystallization of individual structural components of experimental AlSi9Cu3 alloy was determined by evaluation of cooling curves and their first derivatives. Structural analysis was evaluated using a scanning electron microscope. The effect of remelting was manifested especially in nucleation of phases rich in iron and copper. An increasing number of remelts had a negative effect after the fourth remelting, when harmful iron phases appeared in the structure in much larger dimensions.
Variable speed and low voltage electrical drives are commonly operated by frequency converters. According to recent developments, there is a trend in the area of semi-conductors, that switching frequency and voltage slew rate will increase significantly. The aim of these semiconductors is to reduce the switching losses and to increase the switching frequency, which enables to reduce the size of passive components in the power- electric circuit. This results in less material effort and lower cost, for the power electronic component. However, electric motors operated by high slew rate inverters show problems in the winding insulation, which have to be analyzed. Such problems are well known for high voltage machines. Due to the increasing slew rate, this problematic occurs in low voltage machines nowadays as well. Here, the influence of fast switching semiconductors on the winding insulation system is studied, using accelerated ageing tests with fast switching high-voltage generators.
In this paper ∼16 μm-emitting multimode InP-related quantum cascade lasers are presented with the maximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T0) 272 K. Two types of the lasers were fabricated and characterized: the lasers with a SiO2 layer left untouched in the area of the metal-free window on top of the ridge, and the lasers with the SiO2 layer removed from the metal-free window area. Dual-wavelength operation was obtained, at λ ∼ 15.6 μm (641 cm−1) and at λ ∼ 16.6 μm (602 cm−1) for lasers with SiO2 removed, while within the emission spectrum of the lasers with SiO2 left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO2 layer showed ∼15% lower threshold current than these ones with the SiO2 layer. The optical powers for lasers without SiO2 layer were almost twice higher than for the lasers with the SiO2 layer on the top of the ridge.
This paper presents a review of models of the current transport in different kind of heterojunctions (HJs) and their characteristics. In order to effectively deduce the dominant electron transport for the HJs based on ZnO or Zn1−xMgxO layers grown on Si substrate by MBE a comparison is performed – which type of the HJ exhibits better electrical properties. The current–voltage characteristics for the studied HJs were measured within 280–300 K. The transport properties of the HJs are explained in terms of Anderson model with reference to aforementioned current transport models. It is found, that the mechanisms of current transport for all of the studied HJs are similar. At a low forward voltage bias the tunneling current dominates while at medium voltage bias (0.5–1 V) multitunneling capture-emission prevails with the electron trap located at 0.1–0.25 eV below the bottom of a ZnO (Zn1−xMgxO) conduction band. Beyond this voltage bias space charge limited current governs the current transport.