Vickers Hardness Of Materials Research Articles

A unified sharp indentation method for obtaining stress-strain relations, strength and Vickers hardness of ductile metallic materials

Combining dimensional analysis and the definition of Vickers hardness (HV), an integrated prediction model (IPM) for determining the stress-strain relation, strength and Vickers hardness of ductile metallic material is established. The dimensionless functions in the model are determined by using finite element analysis (FEA). The accuracy of the model predicted load-depth relations, Vickers hardness and stress-strain relations are verified within a wide range of imaginary materials via FEA. Moreover, on the basis of the experimental sharp indentation load-depth data for 10 ductile metallic materials from the references, the stress-strain relations, ultimate tensile strength and Vickers hardness of the materials, which predicted by IPM are similar to the uniaxial tensile or hardness testing results. Likewise, the simulated load-depth relations agree well with the sharp indentation experiments results.

Effects of graphene content on the microstructure and mechanical properties of alumina-based composites

In this work, alumina-graphene (Al2O3-G) composites with graphene contents ranging from 0.5 to 3% were prepared by stepwise feeding ball milling and hot pressing. The influences of graphene content on the microstructure and mechanical properties of Al2O3-G composites were investigated. Results showed that the densification, grain sizes, flexural strength, fracture toughness and Vickers hardness of materials increased firstly and then decreased with increasing graphene contents. When the graphene content was 1%, the value of each performance parameter reached the maximum. The average grain size of material decreased from 991 to 551 nm as the graphene content increased from 0 to 1%, but it increased to 863 nm when the graphene content was 3%. The flexural strength, fracture toughness and Vickers hardness of composites with graphene content of 1% increased to 763.5 MPa, 7.4 MPa m1/2 and 21.28 GPa. Compared with the Al2O3, the fracture strength and toughness of the composites increased by up to 54.63 and 65.54%. Analysis suggested that the strength of Al2O3-G composites was mainly related to the grain size and preexisting microflaws.

Study on Relationship between Material Vickers Hardness and Yield Stress of A508 Nuclear Material

It is difficult to directly obtain the mechanical properties of local materials of actual engineering structure (such as welded joints) by traditional mechanical test. Indentation test and ABAQUS finite element test were used in this paper, the relativity between Vickers hardness and yield stress of nuclear material A508 were studied, and a new method of using material surface Vickers hardness to acquire material properties was established. It can be used in the welded lines of nuclear dissimilar metal welded joints to obtain material parameters of mechanical property uneven zone of welded joints, and this new method was supported for complex engineering structure material mechanical parameters.

Analysis of the indentation size effect on the hardness measurements of materials

The influence of the indentation size effect on the hardness measurements of materials using indentation method was studied. A method for determining and comparing the hardness of two different materials with studying the indentation size effect was developed. To identify the influence of the indentation size effect on the Vickers hardness of materials with different levels of hardness two-dimensional parameters α and γ were proposed.

OS0602 高強度鋼の超高サイクル域における疲労寿命の推定(OS6-1 基礎疲労特性と試験法・評価法,OS-6 金属材料の超高サイクル疲労と信頼性評価)

A new prediction method for fatigue life in very high cycle regime was proposed based on the Paris power law. Exponent m and coefficient C in the power law obtained from experimental S-N data showed a good linear relation on a log-log diagram. Also, the exponent m was explained by the Vickers hardness of materials. Proposed prediction method was in form of Basquin's equation explicitly included an inclusion size and hardness of material. The new method was compared to the prior prediction methods and gave a fairly good agreement with the experimental data.

3-sheet structure of Inconel 718 superalloy processed by LBW/SPF and its load response

The 3-sheet structure of Inconel 718 superalloy will be used in flying vehicles as heat resisting and shielding structure due to its lightweight, high strength and stiffness. The 3-sheet structure of Inconel 718 superalloy processed by LBW/SPF (laser beam welding/superplastic forming) technology exhibited good configuration and uniform thickness distribution. The LBW parameters for 3-sheet structure were as follows: Pulse frequency was 32 Hz, impulse duration 3 ms, peak power per pulse 4500 W, and welding speed 180 mm/min. The SPF parameters were as follows: Temperature T=965°C, forming pressure P=4.2 MPa, and forming time t=130 min. The microstructure in weld fusion zone was constituted of austenite dendritics and Laves phase precipitated in interdendritics. After the SPF process, austenite dendritics in the weld fusion became coarser and most of Laves phases were dissolved and turned into δ precipitated phase, but a few of Laves phases were still reserved. And Nb concentration in dendritics increased to 5.42% compared to 2.82% in as-weld condition. Weld metal Vickers-hardness increased from 331.63 in as-weld condition to 391.74 in post-SPF condition which was closed to the base material Vickers-hardness of post-SPF. Grain size of base material grew slightly and an amount of precipitated phase appeared in the base material undergoing SPF process. The tensile test results of base material showed that tensile strength increased obviously and the ductility decreased slightly after SPF process. Load response test results indicated that the 3-sheet structure possessed good resistance to compression and bending load. Accordingly, the LBW/SPF technology is an appropriate forming technique for the 3-sheet structure of Inconel 718 superalloy.

Effect of residual stresses on fatigue strength of severely surface deformed steels by shot peening

The compressive stress distribution below the specimen surface of severely surface deformed steels by shot peening was investigated by using laboratory X-rays and high-energy X-rays from a synchrotron radiation source, SPring-8 in the Japan Synchrotron Radiation Research Institute. Medium carbon steel plates were heat treated in two different conditions. The Vickers hardness of materials A and B after heat treatment is 408 and 617 HV, respectively. The specimens were shot peened with fine cast iron particles of the size of 50 μm. The coverage was selected to be 5000%. For the synchrotron radiation, by using the monochromatic X-ray beam with several energy levels, the stress values at the arbitrary penetration depth were measured by the constant penetration depth method. The shot-peened specimens were fatigued under four-point bending. The improvement of fatigue strength of material A was not so large because of large surface roughness. On the other hand, for material B, the surface roughness was smaller and the fatigue strength was higher than that of ground specimens.

Fabrication and properties of machinable 3Y–ZrO 2/BN nanocomposites

3Y–ZrO 2/BN ceramic composites with nano-sized BN dispersoids ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing turbostratic BN (t-BN) coating 3Y–ZrO 2 powders, which were prepared via in situ reaction between boric acid and urea on the surface of 3Y–ZrO 2 particles in nitrogen gas. XRD analysis and TEM observations revealed that the nano-sized turbostratic and hexagonal BN (t/h-BN) particulates were dominantly dispersed at ZrO 2 grain boundaries. Vickers hardness of materials decreased directly with an increase of BN content. The fracture strength and the fracture toughness were considerably improved, in comparison to corresponding 3Y–ZrO 2/BN microcomposites. The nanocomposites with BN content more than 20 vol.% were ready for machining. The preliminary information on the relationship between microstructures and properties are provided.

The use of a vickers indenter in depth sensing indentation for measuring elastic modulus and vickers hardness

Depth sensing indentation is a powerful experimental technique for determining mechanical properties of materials. In this work a computational routine was developed based on Oliver-Pharr method for measuring a more precise values of elastic modulus using a Fischerscope H100 depth sensing indentation apparatus, with a Vickers indenter. This computational routine aims also to measure Vickers hardness, as the equipment does not have software for this purpose. From indentation data it was possible to determine initial unloading stiffness, contact depth, projected contact area, reduced modulus, elastic modulus and Vickers hardness of materials. The validity of the routine was verified analyzing two coatings and nine bulk specimens with different elastic-plastic behaviors. It was verified that the elastic moduli determined through the software of the equipment resulted in great discrepancies when low loads were applied. A good estimate of the elastic moduli of the tested materials is given by the developed routine. For several testing loads, the diagonals determined by means of analytical procedure were compared with the same diagonals measured by image analysis. A good estimate of the Vickers hardness of the above-mentioned materials is given by the developed routine using different testing loads.

Machinable Al 2O 3/BN composite ceramics with strong mechanical properties

Al 2O 3/BN composite ceramics with nano-sized BN dispersions ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing α-Al 2O 3 powders with turbostratic BN (t-BN) coating, which was prepared through chemical processes using boric acid and urea. SEM observations revealed that the nano-sized hexagonal BN (h-BN) particulates were homogeneously dispersed within Al 2O 3 grains as well as at grain boundaries. Vickers hardness of materials decreased with an increase in BN content. The fracture toughness was improved but the fracture strength had a small decrease, in comparison to Al 2O 3 monolithic ceramics. The nanocomposite ceramics with BN content more than 20 vol.% exhibited excellent machinability, which could be drilled using conventional hard metal alloy drills. Drilling rates and normal forces demonstrate the ease of machining of these materials. The preliminary information on the relationship between microstructures and properties are provided. The mechanism of material removal is also discussed.

A Study On the Prediction of Seizure Behavior of Steels with Molecular Film Lubrication at Low Temperature in a Vacuum

In order to investigate the seizure mechanism of sliding components, a series of friction tests were carried out by sliding a steel ball against a carbon steel plate lubricated with a LB molecular film in a vacuum of 10−4 to 10−2 Pa at the temperatures from 20K to 300K. The Vickers hardness of materials at 20K was also measured. The results indicate that initial times of seizure are strongly correlated with the low temperature hardness of the materials. There exists a critical value of initial temperature Tc for certain mating materials, below which the materials will not seize. The critical temperature is determined by the mechanical properties of the metals and not by surface lubrication. An empirical qualitative expression is introduced to give the relationship between the initial time of seizure and friction conditions, material properties and surface lubrication. The average temperature of friction surface was estimated by calculation. The calculated results show that the critical temperature for friction surface is near the melting point of mating materials. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Test of Hot Hardness

The testing of hot hardness is recently widely practised and drawing attention as a convenient way to find the mechanical properties of engineering materials, e.g. tensile strength, creep strength and creep rupture strength at an elevated temperature. There are two types of apparatuses for testing hot hardness that are now available in Japan to measure the Vickers hardness of materials, both metallic and non-metallic, and the measured values of the hot hardness are greatly variable depending on the measuring conditions and methods. In order to obtain the reliable values of hot hardness it is absolutely necessary, therefore, that the measuring conditions and method will be carefully studied. We have performed a number of experimental studies regarding the testing procedures and the conditions in connection therewith, and have been able, thanks to the cooperation of twelve research laboratories, to obtain a criterion for proper conditions and methods for the testing of hot hardness.