Papers by Keyword: Yield Strength

Abstract: Two grades of Fe-Cr-Ni-Al-Ti-Mo maraging steels, with a different titanium content, were investigated. Particular attention was given to the correlation between the precipitated phases and the yield strength. Synchrotron X-ray diffraction, small-angle neutron scattering and atom probe experiments were performed to determine the crystal structure, shape, size distribution, chemical composition, particle number density and volume fraction of precipitates. Both alloys show a strong increase in strength after an aging treatment, which is attributed to the co-precipitation of two different intermetallic phases. Strengthening by a single precipitation of β-Ni (Al,Ti) particles induces a saturation of yield strength around 1600 MPa above a volume fraction of 6 %. The improvement of yield strength is then obtained by introducing a nanoscale co-precipitation of η-Ni₃(Ti,Al) phase.

Abstract: The technical and commercial development of Thixomolding^® of magnesium (Mg) alloys is described. Based on the MIT semi-solid casting discovery, Dow Chemical adaption to Mg and Thixomat technical findings, Thixomat commercialized this process world-wide with Japan Steel Works (JSW) and numerous licensees in 13 countries. Some 480 Thixomolding machines have been commissioned by JSW to produce a wide range of parts for application in the communication/electronic, auto, sporting goods and hand-held tool markets. The advantages over conventional casting of Mg have been established in cleanliness, safety, worker comfort, machine portability, longer die life and reduced scrap. The competiveness of Thixomolding Mg has been enhanced by more durable and less expensive machine parts, longer die life, higher raw material yields by using hot nozzles and amenability to using recycled Mg scrap. The portability of this “foundry inside a machine” and availability of pre-owned machines allows quick set-up of Thixomolding operations. Several technical advances in Thixomolding are described. Solids content was optimized. Hot nozzles increased the part yield to >90% of the granule Mg alloy feed. Special steel barrels and liners are available to substitute for expensive Superalloys. In addition to conventional AZ91D and AM60, a wide range of Mg alloys can be Thixomolded. With Dead Sea Magnesium, AM70-TH and AJX810-TH were developed for improved ductility or creep strength. Low porosity and fine grain size of Thixomolding open the door to blister-free thermomechanical processing (TTMP) to boost the tensile and fatigue strength and ductility.

Abstract: To compare mechanical properties of three commercial NiTi orthodontic round wires, three commercial brands of NiTi round wire (Nic-China, Ormco-USA, and Smart-Thailand) with sizes 0.014’’, 0.016’’, and 0.018’’were studied. Five specimens each size of each brand were used to test mechanical properties; unloading force (N), spring back (mm), and yield strength (N/mm) with three-point bend test using an Instron Universal Testing Machine. Kolmogorov-Smirnov test and one-way ANOVA were employed to test the differences among groups with statistical difference at p<0.05.The average unloading force from lowest to highest were Ormco, Smart and Nic with 0.014”, Smart, Ormco and Nic with 0.016”and Smart, Nic and Ormco with 0.018”, respectively. The Nic brand had the highest value of unloading force, spring back, and yield strength in all wire sizes, except unloading force 0.018” Ormco and spring back 0.018” Smart. There were no statistically significant differences in unloading forces among all wire sizes. The three brands of commercial orthodontic NiTi wires presented similar unloading force, spring back, and yield strength properties. These mechanical properties are related to lower rates of deformation and are appropriate to be used in the initial phase of orthodontic treatment.

Abstract: In the present investigation, a physically based numerical model was developed to predict the yield stress of Al-7Si-Mg cast alloy during processing. It covered the integrated unit step models of the physical metallurgy of solidification, solid-state of homogenization, and structural hardening of precipitation. The as-cast microstructure of Al-7Si-Mg alloy was calculated based on the cellular automaton method and the evolution of the precipitated phase during aging process was achieved by a precipitation kinetic model involved nucleation, growth and coarsening. The yield stress prediction was achieved by a strengthening model including the effects of as-cast microstructure, solution strengthening and precipitate hardening. The predictions of this model were verified by comparing with experimental measured yield stress which shows that this model is successfully applied to predict the yield stress evolution of Al-7Si-Mg cast alloy.

Abstract: The study deals with the development of highly porous undegradable ceramics based on silicon nitride as potential replacement of trabecular bone. These materials were produced using replication method with polyurethane foams as pore-forming agents to achieve similar porous structure to trabecular bone. Prepared porous ceramics had a bimodal pore structure with macro-pores larger than 200 μm and micro-pores smaller than 1 μm in diameter, which are necessary for tissue ingrowths, cell adhesion, adsorption of biological metabolites and nutrition delivery in organism. The microstructure and local mechanical properties (Young’s modulus and Yield strength) were evaluated and compared with human trabecular bone. Results showed that studied porous materials have satisfactory porosity and pore sizes for trabecular bone replacement. Young’s modulus of bone was 12.6 ± 2.23 GPa and porous silicon nitride samples ranged from 10.9 ± 3.38 GPa to 12.9 ± 1.13 GPa. The values of Yield strength of trabecular bone was determined as 493 ± 30.7 MPa and the values of porous samples varied from 250 ± 19.3 MPa to 558 ± 36.5 MPa. Young’s modulus and Yield strength increase with increasing of the pre-sintering temperature and multiple infiltrations.

Abstract: Brazing is extensively used in liquid rocket engines for realizing various subsystems. In the case of cryogenic engines, brazing operation is done to realize the gas generator. Gas Generator is one of the major systems of cryogenic engine. It generates and supplies hot gases required for running turbine of main turbo pump. This uses liquid oxygen and gaseous hydrogen as propellant combination. Combustion chamber of Gas Generator is of double walled construction with the cylindrical outer shell of transition class ICSS-0716-301 austenitic-martensitic stainless steel and inner shell of ICSS-1218 321, aTi stabilized austenitic stainless steel material brazed together with Fe-Ni-Mn type braze alloy at a temperature of 1180°C. This temperature can cause the grain growth and related issues to the base material. Thus the present work focuses on the effect of the brazing/thermal cycle on mechanical properties and microstructure of the base materials in post braze condition. The results obtained on metallurgical/mechanical behavior of the material showed the different grain growth patterns in inner and outer shell materials. This helped in understanding the effect of brazing condition on the changes in mechanical properties of base materials.

Abstract: Ti-6Al-4V alloy is widely used in Aerospace applications owing to its high specific strength, low coefficient of thermal expansion and good corrosion resistance. Presence of interstitial elements in the alloy has some significant effects on its properties. However the poor notch toughness and cryogenic ductility restricts the usage of Ti-6Al-4V for temperatures lower than 77 K (-196 °C). The Extra Lower Interstitial grade alloy was developed in order to improve the notch toughness and cryogenic ductility of the Ti-6Al-4V alloy. In this refined grade, the interstitials, Oxygen and Carbon are controlled to a maximum limit of 0.12% and 0.08% respectively as compared to a maximum of 0.2% and 0.1% of standard Ti-6Al-4V alloy. In this study, the ELI grade of Ti-6Al-4V rods from three different manufacturing sources were subjected to tensile test at liquid hydrogen temperature at 20 K (-253 oC). The tensile properties obtained are compared and analyzed. The obtained ductility at 20 K is observed to have close relation with the chemical composition and interstitial content and compared with the Ti5Al2.5Sn-ELI which is ideally suitable for low temperatures upto 20 K, owing to its single phase HCP structure. A correlation has been made between the ductile properties and microstructure. By close control of chemical composition and mechanical working, Ti6Al4V-ELI can be used for temperatures lower than 77 K (-196 oC), which is otherwise is forbidden. This paper details the test data obtained from three different compositions of Ti6Al4V-ELI at 20 K, which enables the usage of this material for temperatures lower than 77 K (-196 °C) upto 20 K.

Abstract: Al-Cu-Mg-Ag alloy 2139 is a wrought alloy that is heat-treatable and used in aerospace constructions. This is mainly due to the addition of silver in the alloy. Hot-tearing is a problem for casting wrought alloys with conventional liquid casting techniques. The risk is reduced by using rheo-high pressure die casting (R-HPDC) to allow the alloy to be used for near-net shape forming of components. This study investigates the segregation characteristics of R-HPDC alloy 2139. The effects of segregation on the age-hardening response as well as the tensile properties are studied. The chemical composition differences across the casting were found to aid in correlation of results. It is found that segregation occurs in three dimensions, namely from the surface to the centre of the casting, as well as across the width and length of the casting.

Abstract: Corrosion of steel bars has become the primary cause for the concrete durability problem. Stress concentration due to uneven corrosion affect the mechanical properties of reinforced bar. This paper take HRB400 rebar for example to analyze the effect. FEM is conducted to analyze the effect of corrosion pit position on yield strength and ultimate strength. The result shows that corrosion pit in transverse rib has a different effect on yield strength and ultimate strength, while corrosion pit in longitudinal rib and reinforced column make yield strength and ultimate strength of reinforced bar decrease in varying degrees.

Abstract: In the present method the effect of welding speed, axial force, tool rotational speed and shoulder penetration on the mechanical properties of Aluminium alloy 6061 butt joint produced by Friction Stir Welding (FSW) is analyzed. The mechanical behavior properties like Yield Strength, Tensile Strength and % of Elongation has been tested using 5 mm thick plate. The tool used for conducting the experiment was High Speed Steel (HSS). Tensile Strength, Yield Strength and Percentage of Elongation of FSW Al alloy 6061 has been evaluated under different processing condition using Taguchi’s design. The optimum results had been obtained using main effects plot using S/N ratio values. Tool rotation speed has been found dominant factor for Tensile Strength followed by feed and shoulder penetration. Shoulder diameter shows the minimal effect on Tensile Strength compared to other parameters.