High TiC Content Research Articles

The ‘Mediaeval Warm Period’ drought recorded in Lake Huguangyan, tropical South China

The geochemistry of dated sediment cores from Lake Huguangyan (21°9′N, 110°17′E), tropical South China, reveals distinct stratigraphical patterns in total organic and inorganic carbon (TOC, TIC), biogenic silica (BS) and total nitrogen (TN) over the past 1400 years. In this hydrologically closed lake, TIC variations may re‘ ect changes in the precipitation/evaporation ratio, which controls the evaporative enrichment of carbonate. TOC, BS and TN in the sediment are proxy indicators of lake productivity and nutrient input, which we believe are linked to local precipitation. High TIC content correlates with low concentrations of TOC, BS and TN, and indicates two drought episodes dated to ad 670–760 and ad 880–1260 in the sediments of Lake Huguangyan. Local historical chronicles support these data, suggesting that the climate of tropical South China was dry during the ‘Mediaeval Warm Period’ (MWP) and wet during the ‘Little Ice Age’ (LIA). The detected MWP drought is temporally correlated with evidence for lower precipitation on the Guliya (China) and Quelccaya (Peru) ice caps, and with increased salinity in Moon Lake (US Great Plains).

Ａｌ２Ｏ３‐ＴｉＣセラミック工具におけるフレーキング現象

The flaking phenomenon often appearing in Al2O3-TiC ceramics tools in turning of alloyed tool steels was studied, as a continuation of the previous reports. The Al2O3-TiC ceramics having 10-50 mass%TiC and different grain size of TiC were prepared by hot-pressing, and the ceramics tools were subjected to turning tests of SKD11 (ASTM, HB).It was confirmed that the tools with lower or higher TiC content and with coarser TiC grains showed generally low resistance to flaking. It was found that the flaking originated from a micro-crack formed on the pre-honing surface. The formation of the micro-crack was considered as follows. In the case of the tools with lower TiC content, the amount of flank wear was apt to increase, leading to the increase in the resultant cutting force which sheared the crater surface. On the other hand, in the case of tools with higher TiC content, the amount of adhesion on the pre-honing surface, that is, the amount of the surface wear (crater wear) became larger since the reaction between work and tools during tests was enhanced, resulting in the generation of tensile stress on the pre-honing surface in the course of removing off of adhesion.

WEAR OF CERAMIC TOOLS WHEN MACHINING CAST IRON

ABSTRACT Five commercially available ceramic tool inserts were used for studying the machining characteristics of grey cast iron. These inserts from three suppliers were shown to behave as two groups. The first group containing Al203 and Al203/Zr02 showed low wear rates over a wide range of cutting speeds and these wear rates were essentially speed independent. This group showed considerable fracture tendency in the speed range 250m/min - 500 m/min. Alumina tools containing TiC/TiN showed higher wear rates which were both speed and TiC content dependant. High TiC content tools demonstrated high wear rates at low speeds and vice versa. TiN appeared to have little, if any, effect on wear rate. The presence of TiC and TiN also appeared to suppress the fracture tendency in the speed range 250m/min - 500 m/min.

Laser treatment of sintered TiC-steel alloys

1. Laser treatment of TiC-5Kh6VM2 steel alloys leads to a significant increase in hardness in the zone of laser action. The maximum effect of laser hardening is obtained for alloys containing up to 30% TiC. 2. The addition of titanium carbide to the steel leads to an increase in the depth of the zone of laser action as the result of a change in the character of heat dissipation. 3. The increase in hardness of the alloy with 10% TiC is caused by the significant redistribution of the carbide phase, the increase in its degree of dispersion, and additional alloying of the steel binder. 4. After laser treatment of alloys containing 10% TiC their relative wear resistance e is four to five times higher than after through oil hardening. The e of the alloy with 10% TiC is also higher than the e of alloys with a higher TiC content. 5. The tendency toward crack formation of alloys with titanium carbide limits its content to 10%.