Effects of temperature and load during hot impression behavior of Cr-Ni stainless steel

Austenitic Stainless steels are majorly used because of their high resistance to aqueous corrosion and high temperature properties. Some major applications of stainless steels at high temperatures include engine and exhaust components in aircrafts, recuperators in steel mills, and pulverized coal injection lances for blast furnaces. In all the above said applications, the components are constantly subjected to loads and high temperatures. This makes the study of their creep behavior very important to decide the life of the component. Cr-Ni stainless steel was used as a starting material, and hot impression creep test was performed on cylindrical samples of 10 mm height and 15 mm diameter for a dwell time of 150 min at two different loads of 84 and 98 MPa and at two different temperatures 450 and 500 °C. The time vs. indentation depth was plotted, and creep rate was calculated in each case. It was observed that with an increase in time, creep rate increased in the primary creep region and remained almost constant in the secondary creep region irrespective of temperature and load. The indentation depth and creep rate increased with an increase in load and temperature.

Interface Strengthening of α-Mg/C14–Mg2Ca Eutectic Alloy

This study investigates the effect of the α/C14 interface on the creep strength of α-Mg/C14–Mg2Ca eutectic alloy at 473 K under a stress of 40 MPa. The α/C14 interface is composed of terraces and steps, with terraces parallel to the (1101)α pyramidal plane of the α-Mg lamellae and to the (1120)C14 columnar plane of the C14–Mg2Ca lamellae. The creep curves of the alloy exhibit three stages: a normal transient creep stage, a minimum creep rate stage, and an accelerating stage. The minimum creep rate is proportional to the lamellar spacing, indicating that the α/C14 lamellar interface plays a creep-strengthening role. In the high-resolution transmission electron microscopy image captured of the specimen after the creep test, <a> dislocations can be mainly seen within the soft α-Mg lamellae, and they are randomly distributed at the α/C14 interface. In contrast, dislocations are rarely introduced in the hard C14–Mg2Ca lamellae. It is deduced that the α/C14 interface presents a barrier to dislocation gliding within the α-Mg lamellae and does not help rearrange the dislocations.

Fabrication and Nanomechanical Characterization of Thermoplastic Biocomposites Based on Chemically Treated Lignocellulosic Biomass for Surface Engineering Applications

Diverse applications of polymeric materials have prompted development of eco-friendly, efficient, and economical materials. These characteristics can be obtained by incorporating appropriate fillers in the polymeric matrix. The objective of this work is to investigate impact of aqueous glycerol (Gly) treated rice husk (RH) on surface mechanical properties of produced biocomposites. RH was treated with aqueous Gly (75 wt%) and compounded with low density polyethylene (LDPE) at different loadings (10, 20, and 30 wt%). The resulting mixture was thermally pressed in molds to fabricate biocomposites. Surface mechanical properties such as elastic modulus, hardness, creep rate, and plasticity of biocomposites reinforced with untreated and treated RH were investigated using nanoindenter. Experimental values depicted that hardness (H) and elastic modulus (Es) of treated biocomposites were higher than untreated ones. Treated biocomposites showed the noticeable improvement in elastic modulus by 24 and 37% compared to untreated biocomposites at 20 wt% loading and neat LDPE, respectively. Reductions in the creep rate by 20 and 14% were observed for untreated and treated biocomposites, respectively, in comparison to the neat LDPE. H/E ratio was increased by 23 and 18% for treated and untreated biocomposites, respectively, as compared to virgin LDPE. Furthermore, mechanical and structural properties of untreated and treated RH are reported based on nanoindentation response and Fourier transform infrared spectroscopy (FTIR) techniques The study indicated that aqueous glycerol pretreatment can partially strip off non-cellulosic constituents from lignocellulose matrix to generate cellulose-rich pulp for engineered composite applications.

Creep Deformation Property and Creep Life Evaluation of Super304H

Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increase in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C and above. In the short-term, at 600°C, creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing the maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C. Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into accounts of the change in slope of stress vs. time to rupture curves was demonstrated.

COMPARATIVE EVALUATION OF THE CREEP OF PISTON ALUMINUM ALLOYS

The paper deals with the issues of reliability of piston materials in the process of increasing engine power. It is precisely the increase in the liter power of engines while ensuring environmental and economic requirements that is today one of the main areas of work in engine manufacturing. Studies have shown that material creep has significantly affects on the reliability of internal combustion engine parts. The most thermally loaded engine element is a piston. The main critical areas for it can be identified: the edge of the combustion chamber, the area of the piston rings and the piston skirt. The appearance of seizures on the piston skirt is sometimes observed even during the engine initial tests at the engine power increasing. Thus, we can speak about the relevance of the problem of identifying the reasons for reaching the critical state of the piston material. Based on these data, it becomes possible to develop measures to ensure the reliable operation of the piston. Among the most common materials for the manufacture of pistons are aluminum alloys AL25 and AK4. The chemical composition of these alloys varies considerably. The study obtained coefficients for calculating the creep rate for these materials. The identification of the calculation of the creep deformation of aluminum alloys at different stress levels, for different temperatures is carried out. The upper boundary of the region of model adequacy in terms of temperatures and stresses is determined. The creep rate of aluminum alloys is analyzed at different temperatures. In the conclusions, a comparison of the piston materials is made and the advantages of the AK4 alloy in comparison with the AL25 alloy, which are coming out when the engine power is increased, are indicated. The direction of further research is also indicated, which is associated with the analysis of the deformation of the considered materials at the first stage of creep.

Creep on the Sargent Fault over the Past 50 Yr from Alignment Arrays with Implications for Slip Transfer between the Calaveras and San Andreas Faults, California

ABSTRACT The 55-km-long Sargent fault connects the creeping Calaveras fault with the locked San Andreas fault through the Santa Cruz Mountains west of Gilroy, California. The position of the Sargent fault between these two faults may have implications for slip transfer and strain accumulation between a creeping and locked fault. The detection and measurement of creep on the Sargent fault would indicate where interseismic strain is accumulating adjacent to these neighboring faults. In 1969, two alignment arrays separated by 3.7 km were installed across the central section of the Sargent fault to investigate potential creep. These arrays were measured in 1970 and 1975, and comparison of these measurements yielded a creep rate of 3.4 ± 0.6 mm/yr across two fault strands in the northern array; results from the southern array were never published. In 2019 and 2020, we resurveyed both arrays using a total station and analyzed the results to determine accumulated fault creep. Our results show that between 1970 and 2020, a period of 49.3 yr, the northern array was dextrally offset 164 ± 25 mm across the same two fault strands that were active in the 1970s, yielding an average creep rate of 3.3 ± 1.3 mm/yr. Thus, it appears that the 5 and 50 yr creep rates at this site are similar. The southern array, which may not span the entire fault zone, was dextrally offset 84 ± 13 mm across two fault strands between 1970 and 2019, yielding an average creep rate of 1.7 ± 0.8 mm/yr over 48.9 yr. These recent surveys document continued creep on the Sargent fault, which may reduce seismic strain accumulation and therefore seismic hazard. However, continued aseismic slip on this fault may result in the redistribution of stress and strain to adjacent faults and should be an area of continued study.

Uniaxial Compression Mechanical Properties of Foam Nickel/Iron-Epoxy Interpenetrating Phase Composites

The damage process and failure mechanisms were analyzed by a series of quasi-static compressive experiments of seven materials including pure epoxy (EP), three different PPI (pores per linear inch) foam nickel-iron, and three different PPI foam nickel/iron-epoxy interpenetrating phase composites (IPC). Plotting the stress–strain curves of different materials, their change rules are discussed, then the effective elastic modulus and yield limit of the materials are provided, and the energy absorption properties of different materials are analyzed by the stress–strain curves. It was found that the effective elastic modulus and specific stiffness of the three IPC materials were higher than pure foam nickel-iron. The brittleness of epoxy can be obviously changed by selecting a suitable PPI foam nickel-iron composited with it. The unit volume energy absorption rate of foam nickel/iron-epoxy was significantly higher than pure epoxy and pure foam nickel-iron. It was also found that the energy absorption rate decreased with the increase in PPI. The stress relaxation rate decreased first and then increased with the increase in PPI. The creep behavior of the three composites was obvious in the creep elastic stage, and the creep rate increased with the increase in PPI. The creep rate decreased with the increase in PPI in the creep transition stage.