Papers by Author: Lin Geng

Abstract: The hot compression behavior of in situ TiB whiskers reinforced Ti6Al4V (TiBw/Ti6Al4V) composites with a novel network microstructure is investigated in the temperature range of 900-1100°C and strain rate range of 0.001-10 s^-1. The results show that all the stress-strain curves of the composites display peak flow, softening and steady-state. Moreover, the peak flow stress decreases with increasing temperatures and decreasing strain rates. Processing map of the composite is constructed using the dynamic material model (DMM). Dynamic recrystallization (DRX) of α phase is observed in the deformation region corresponding with peak efficiency of the processing map. However, the flow instability region ranged from 900 to 1100°C at strain rates higher than 1.0 s^-1 should be avoided.

Abstract: Crystallization behavior of melt aluminum on the surfaces of SiC whisker (SiCw) was analyzed based on the consideration to obtain the SiC-Al interfaces with the lowest energy in SiCw/Al composite. The interfacial structure was investigated to determine whether a specific orientation relationship exists between SiC and Al. Analysis results indicate that four kinds of orientation relationships possibly exist between SiC and Al when only the <110> crystal direction of the aluminum is considered as the firstly formed crystal direction along the concave joint line of <110> of the SiC whisker. Interfacial atom match bonding models were set up in theory and one kind of crystal orientation relationship has been proved by our previous experimental result.

Abstract: With Third Wave AdvantEdge FEM software, an equivalent finite element model in tapping has been built, making a simulation study of the chip curling of titanium alloy TC4 and analyzing the influnce of a tap hook angle and chip flute shape on chip curling. Based on the simulation study above, the modified-tooth taps made of high-speed steel W9, which have two types of chip flute shape with a chamfer angle of 7°30´and respectively, were developed and the comparative tests of tapping TC4 have been done. The results indicates that the chip removal effects in hand tapping with the standard flute shape and respectively are on the same level, but the tapping torque has become smaller and more effective to a chamfer angle of .

Abstract: The mechanical model of the tapping torque and the friction one were established based on Theoretical Research of Tapping Forces. A series of standard taps with a cutting cone angle of 7°30′ were prepared from high-speed steel W9 and used to tap Nickel-based superalloy GH4169.It was found that the friction torque was about 45% of the total torque as tapping with the standard taps. Friction torque is the main reason in tapping difficult –to-cut materials.

Abstract: In this paper, BaPbO3(5Vol.%)/2024Al composite was fabricated by powder metallurgy method. Nanosized Pb particles were formed from the in-situ reaction between BaPbO3 and 2024Al, and mainly distributed homogeneously inside grains. The hot compression deformation of the composite at different temperatures was performed. The microstructure evolution of the 2024Al matrix and dynamic mechanical analysis (DMA) of the composite were made to investigate the effect of liquid Pb on the hot deformation. The results show that the presence of the liquid phase reduces deformation resistance by decreasing dislocation pileups, and simultaneous decrease in Young’s modulus of the composite.

Abstract: In this work, Ti5Si3 and TiC particle reinforced titanium aluminide matrix composite sheet was fabricated by rolling and reaction annealing using the starting materials of SiCp/Al composite and pure titanium sheet. The deformation compatibility of both starting materials and microstructure evolution during reaction synthesis were studied. The results show that titanium has the similar deformability with SiCp/Al composite via the introduction of SiC particles and the selection of proper rolling temperature. Titanium aluminide matrix composite reinforced by Ti5Si3 and TiC was synthesized by reactions during the annealing. The reactions include the formation of titanium aluminide matrix by the diffusion synthesis between titanium and aluminum, as well as reinforcements (Ti5Si3 and TiC) by in-situ reaction between SiC and titanium.

Abstract: In this paper, the milling process of WO3 and aluminum particles is studied. Influences of rotate rate, milling time and ball-to-powder weight ratio on the morphology and grain size of the particles are studied by scanning electronic microscope and X-ray diffraction techniques. Al particle size decreases firstly and then increases with increasing milling time, while Al grain size decreases gradually as the milling time increases. WO3 particle is distributed uniformly in Al particles after milling for 9h, and has no marked change as further extension of milling time. With increasing the ball-to-powder weight ratio and rotate rate, both particle size and grain size of Al decreases. milling parameters have almost no effect on the grain size of the WO3 particles.

Abstract: A process of laser cladding of NiCrBSi+2%B4C powder on Ti–6Al–4V substrate to form a coating was carried out, a good coating without cracks and pores was obtained in the process. The microstructure and component of the coating were examined using SEM and EPMA. The interface between the coating and the substrate was metallurgical, The microstructure of NiCrBSi+2%B4C cladding layer consisted of the Ni-based matrix, and the uniformly dispersed reinforcement phases of TiB2, TiC, etc. The microhardness of the coating was measured using a Vickers hardness tester. The average microhardness of the composite coating was HV1200 HV1400, and it was three times higher than that of Ti-6Al-4V substrate.

Abstract: The coefficients of thermal expansion (CTEs) of the 20 vol% SiCp/Al composites fabricated by powder metallurgy process were measured and examined from room temperature to 450°C The SiC particles are in three nominal sizes 5μm, 20μm and 56μm. The CTEs of the SiCp/Al composites were shown to be apparently dependent on the particle size. That the larger particle size, the higher CTEs of the composites, is thought to be due to the difference in original thermal residual stresses and matrix plasticity during thermal loading. The thermal conductivity of the composites also increases with particle size increasing.

Abstract: (α+β)/β phase transformation temperature of a TC11 titanium alloy was confirmed to be 1035°C, which was obtained by three methods including the calculation method, differential scanning calorimetry and metallographic techniques. Based on this result, annealing treatments below and above the (α+β)/β phase transformation temperature were carried out, and the microstructure of the TC11 alloys before and after annealing treatment was analyzed by SEM. The result showed that conventional annealing below 1035°C does not change the Widmanstaten structure of TC11 alloy, though the thickness of α lamellar structure becomes thicker with increasing the annealing temperature. The microstructure of the TC11 alloy treated by annealing above the α+β/β transformation temperature is non-uniform because of the different forming temperature and growing duration of α phase in the TC11 alloy.