Ageing Effect on Hardness and Microstructure of Al-Zn-Mg Alloys

Experimental results of the investigation on the hardness of two Al-Zn-Mg alloys [Al-10.0 Zn-4.0 Mg and Al-8.5 Zn-3.0 Mg (wt pct)] aged in the temperature range 60～310℃ for different intervals of time from 1/4 h to 168 h are presented. Both the alloys were found to show identical behaviour of hardness with ageing time. Alloy with higher Zn and Mg content had higher hardness than the alloy with lower solute content. There were three ranges of temperature in which different types of precipitates formed and affected the hardness. Some of the grain boundaries were found to migrate and precipitate free zone has been observed.

Effect of Hot Deformation on Microstructure and Hardness of In-situ TiB_2/7075 Composite

Hardness of the TiB2/7075 composite increased with increasing deformation temperature. In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about 1 mum in length) and small MgZn2 phases (about 100 nm in size) were precipitated nearby the grain boundaries where the TiB2 particles exist. After deformation at 300 degreesC, some of the large precipitates and all the small precipitates in these area dissolved into the matrix, meanwhile, fine precipitates were formed in grains. After deformation at 450 degreesC, all the precipitates in the annealed composite dissolved into the matrix, and new phases were precipitated in grains. The dissolution of the large fiber-like precipitate makes the saturation level of the matrix increased and leads to an increased solution hardening and natural aging, which contribute much to the hardening effect.

Microstructure characteristics of Ni/WC composite cladding coatings

A multilayer tungsten carbide particle（WCp）-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology.The morphology,microstructure,and formation mechanism of the coating were studied and discussed in different zones.The microstructure morphology and phase composition were investigated by scanning electron microscopy,optical microscopy,X-ray diffraction,and energy-dispersive X-ray spectroscopy.In the results,the coating presents a dense and homogeneous microstructure with few pores and is free from cracks.The whole coating shows a multilayer structure,including composite,transition,fusion,and diffusion-affected layers.Metallurgical bonding was achieved between the coating and substrate because of the formation of the fusion and diffusion-affected layers.The Ni-based alloy is mainly composed of y-Ni solid solution with finely dispersed Cr7C3/Cr（23）C6,CrB,and Ni＋Ni3Si.WC particles in the composite layer distribute evenly in areas among initial Ni-based alloying particles,forming a special three-dimensional reticular microstructure.The macrohardness of the coating is HRC 55,which is remarkably improved compared to that of the substrate.The microhardness increases gradually from the substrate to the composite zone,whereas the microhardness remains almost unchanged in the transition and composite zones.

Effect of Cooling Rate and Vanadium Content on the Microstructure and Hardness of Medium Carbon Forging Steel

This paper reports the effect of cooling rate on the microstructure and hardness of a kind of medium carbon steel microalloyed with two levels of V content （0.15% and 0.28%） after hot deformation by using single compression tests on a Gleeble-3800 thermal simulator. The results show that cooling rate has a significant effect on the microstructure and hardness of the tested steels. Both the fraction of pearlite and hardness increase with increasing cooling rate, whereas a further increase of the cooling rate above a critical value promotes the formation of acicular ferrite （AF）, and thus leads to a decrease of hardness mainly owing to the decrease of pearlite fraction and replacing it by AF and the less effective precipita- tion strengthening. Increasing V content results in a significant increase of hardness, and this tendency enhances with increasing cooling rate until the formation of AF. Furthermore, increasing V content also significantly enhances the formation of AF structure at a lower cooling rate. The results also suggest that by controlling microstructure, especially the precipitation of fine V（C,N） particles through adjusting post- forging cooling, the strengthening and gradient function in one hot-forging part could be obtained.

Influence of Ru on Solidification Behavior, Microstructure and Hardness of Re-free Ni-based Equiaxed Superalloys with High Cr Content

The effect of Ru addition on solidification behavior, microstructure and hardness of Re-free Ni-based equiaxed superalloys with high Cr content has been investigated. With the increase of Ru, the solidus temperature of the alloys and the γ＂ solvus temperature decreased, respectively. However, the liquidus temperatures of the alloys bad no obvious change. The microstructure of the as-cast alloys was mainly composed of γ, γ＇, γ＇/γ＇ eutectic and MC carbides. The γ/γ＇ eutectic was completely dissolved after the heat treatment. The morphology of γ＇ was more cuboidal in heat-treated alloys with increasing Ru. Furthermore, the volume fraction of γ＇ in the as-cast and heat-treated alloys diminished upon the increase of Ru. It was noted that Ru addition changed the segregation behaviors of Cr and Mo in the alloys from positive segregation element to negative segregation element and promotes the segregation degree of W. As the Ru content increased, the magnitude of segregation of the positive segregation elements Ta and Ti increased accordingly. Meanwhile, the magnitude of Al segregation decreased and Ru tended to segregate in the dendrite core. In addition, the hardness of the alloys improved and their porosity reduced with increasing amount of Ru.

Microstructure and properties of Al_(0.3)CrFe_(1.5)MnNi_(0.5)Ti_x and Al_(0.3)CrFe_(1.5)MnNi_(0.5)Si_x high-entropy alloys

In this article, the microstructure, hardness, and corrosion resistance of the Al0.3CrFe1.5MnNi0.5Tixand Al0.3CrFe1.5MnNi0.5Six（x = 0, 0.2, 0.5, 1.0） high-entropy alloys were investigated via X-ray diffraction（XRD）scanning electron microscopy（SEM）, digital display Vickers hardness tester, and electrochemical technique These alloys are mainly composed of BCC solid-solution structure. When adding high content of Ti or Si elemen（x C 0.5）, some intermetallic compounds are found in the microstructure, which makes the alloys have a high hardness, high brittleness, and easy cracking. While the alloys with low content of Ti or Si（x = 0.2） have a hardness of HV 420–HV 430, and its hardness increases about 14 %compared with that of Al0.3CrFe1.5MnNi0.5. Electrochemical results in 3.5 % NaCl solution show that the alloying elements Ti and Si have a negative influence on the corrosion resistance of the Al0.3CrFe1.5MnNi0.5alloys.

The synergistic role of Ti microparticles and CeO_(2) nanoparticles in tailoring microstructures and properties of high-quality Ni matrix nanocomposite coating

In current work,Ni-Ti-CeO_(2) nanocomposite coatings were achieved by co-adding Ti microparticles and CeO_(2) nanoparticles.Designed experiments and COMSOL computer simulation were applied to reveal the synergistic role of Ti microparticles and CeO_(2) nanoparticles in tailoring the spatial microstructures and properties of Ni-Ti-CeO_(2) nanocomposite coating.Unilaterally,the conductive Ti microparticles conducted the growth behavior of Ni grains by current density concentration,distorting electronic feld lines and heterogeneous nucleation.Individual domains consisting of inner nanograins and outer radial columnar grains surrounded Ti microparticles,where Ti microparticles acted as seeds.Ti microparticles tended to be aggregated,leading to spatial heterogeneity of microstructures.Ni deposits buried the Ti microparticles in forms of“covering model”,contributing to the formation of inside voids and rough surface and aggregation of Ti microparticles;on the other hand,the non-conductive CeO_(2)microparticles hardly changed the distribution of current density and electronic feld lines on the cathode surface.Ni deposits buried the CeO_(2)microparticle in forms of“stacking model”,avoiding the inside voids and aggregation of particles.The incorporation of CeO_(2)microparticle brought in microstructure evolutions only on its top side without disturbing the growth behavior of Ni grains on its lateral side or bottom,suggesting the limited effects.This was correlated with the presence of current concentration above the CeO_(2) microparticle at the last stage of burying CeO_(2) microparticle.The co-addition of Ti microparticles and CeO_(2) nanoparticles into Ni deposits exploited the complementary action of the two particles,which gave birth to satisfed spatial microstructures and improved hardness.Ti microparticles took major responsibility for microstructure evolutions,while the CeO_(2) nanoparticles were mainly in charge of the microstructure homogeneity.

Gradient Structured Copper by Rotationally Accelerated Shot Peening

A new technology-rotationally accelerated shot peening（RASP）, was developed to prepare gradient structured materials. By using centrifugal acceleration principle and large steel balls, the RASP technology can produce much higher impact energy compared to conventional shot peening. As a proof-of-concept demonstration, the RASP was utilized to refine the surface layer in pure copper（Cu） with an average grain size of 85 nm. The grain size increases largely from surface downwards the bulk, forming an800 ？m thick gradient-structured surface layer and consequently a micro-hardness gradient. The difference between the RASP technology and other established techniques in preparing gradient structured materials is discussed. The RASP technology exhibits a promoting future for large-scale manufacturing of gradient materials.

Experimental Investigation on Friction Welding of UNS S32205 Duplex Stainless Steel

UNS S 32205 duplex stainless steel specimens were joined by continuous drive friction welding process. The experiments were conducted as per the Taguchi（L16 orthogonal array） method. The friction welding process parameters such as heating pressure, heating time, upsetting pressure, upsetting time, and speed of rotation were fixed with low,medium, and high levels of range based on the machine capacity, and the required knowledge was acquired from the preliminary experiments. The joint characterization studies included micro structural examination and evaluation of mechanical properties of the joints. Microhardness variation, impact toughness, and tensile strength of the joints were evaluated. Neither a crack nor an incomplete bonding zone was observed. The tensile strength of the joints was higher than the strength of the base material, and the friction and upsetting pressures were found to influence the joint strength. The tensile strength of all the welds was observed to be increasing with an increase in the rotational speed. The toughness of the friction welds was evaluated at room temperature and also at subzero（cryo） temperature conditions. The toughness for friction welds was found to be superior to the fusion welds of duplex stainless steel at room temperature and cryo conditions. Weldments exhibited better corrosion resistance than the parent material.