A new class of high‐performance resins of combined molecular structure of both traditional phenolics and benzoxazines has been developed. The monomers termed as methylol‐functional benzoxazines were synthesized through Mannich condensation reaction of methylol‐functional phenols and aromatic amines, including methylenedianiline (4,4′‐diaminodiphenylmethane) and oxydianiline (4,4′‐diaminodiphenyl ether), in the presence of paraformaldehyde. For comparison, other series of benzoxazine monomers were prepared from phenol, corresponding aromatic amines, and paraformaldehyde. The as‐synthesized monomers are characterized by their high purity as judged from ¹H NMR and Fourier transform infrared spectra. Differential scanning calorimetric thermograms of the novel monomers show two exothermic peaks associated with condensation reaction of methylol groups and ring‐opening …

The effect of austenitizing temperature and Cr, Mo and Mn addition on microstructure and mechanical

properties of V microalloyed medium carbon steel has been studied by means of metallography and mechanical

testing. The addition of Cr, Mn and Mo leads to a decrease in yield strength (YS) by approximate 100 MPa in

comparison to the base steel. It is assumed that Mn and Mo increase hardenability by promoting the formation

of bainitic sheaves (BS), i:e: by suppressing the formation of ferrite-pearlite and acicular ferrite (FP-AF). Cr

at the level used in this work is not that e®ective. Presence and packet size of bainitic sheaves decrease

the Charpy V-notch impact energy at 20 ±C (CVN20) in comparison to ferrite-pearlite and acicular ferrite

microstructures.

Historically, applications for traditional phenolic resin/polyurethane materials are limited due to the inherently weak thermal stability of urethane-phenolic linkage and slow reaction rate. A novel concept has been developed to produce phenolic resin/polyurethane copolymers ...

The unique features of polybenzoxazines make them attractive for a wide range of applications. The characteristics of polybenzoxazines such as excellent dimensional stability, lower surface energy, higher Tg, and lower moisture absorption are attributed to the stable intramolecular hydrogen bonding in their network structure. The features make polybenzoxazines excellent candidates for the applications that require near zero shrinkage and high dimensional stability. Polybenzoxazines are formed by the autocatalytic polymerization of benzoxazine monomers. Polybenzoxazines are well known as a new class of thermoset polymers used for high performance applications. They provide the characteristic properties found in phenolic resins, such as high thermal stability, excellent electrical properties, good mechanical properties, and better flame retardancy. Furthermore, they have the advantages …

Activation energy for static recrystallization estimated in this work of 281kJ/mol is in excellent agreement with previously reported data (both experimental and mdeled) and indicates that difusion of Nb in austenite is most probably the rate controlling process

The influence of vanadium and nitrogen on microstructure and mechanical properties of medium-carbon

steels has been studied by means of metallography and mechanical testing. Vanadium addition to the low

nitrogen steel suppresses the formation of ferrite–pearlite following the low reheating temperatures and microstructure

consists of bainitic sheaves. Increasing nitrogen at the same vanadium level promotes the acicular

ferrite formation. For high reheating temperatures, dominantly acicular ferrite structure in both the low

nitrogen and the high nitrogen vanadium steels is obtained. The results suggest that vanadium in solid solution

promotes the formation of bainite. The effect of nitrogen is related to the precipitation of VN particles in

austenite with high potency for intragranular nucleation of acicular ferrite and to the precipitation of V(C, N)

particles in ferrite with high potency for precipitation strengthening. Addition of both vanadium and nitrogen

considerably increases the strength level, while CVN20 impact energy increases on changing the microstructure

from bainitic ferrite to the fine ferrite–pearlite and acicular ferrite.

The influence of vanadium and nitrogen on microstructure and mechanical properties of

medium-carbon steels has been studied by means of metallography and mechanical testing.

Vanadium addition to the low nitrogen steel suppresses the formation of ferrite-pearlite following

the low reheating temperatures and microstructure consists of bainitic sheaves. Increasing nitrogen

at the same vanadium level promotes the acicular ferrite formation. For high reheating temperatures,

dominantly acicular ferrite structure in both the low nitrogen and the high nitrogen vanadium steels

is obtained. The results suggest that vanadium in solid solution promotes the formation of bainite,

whereas the effect of nitrogen is related to the precipitation of VN particles in austenite with high

potency for intragranular nucleation of acicular ferrite and to the precipitation of V(C,N) particles in

ferrite with high potency for precipitation strengthening. Addition of both vanadium and nitrogen

considerably increases the strength level, while CVN20 impact energy increases on changing the

microstructure from bainitic ferrite to the fine ferrite-pearlite and acicular ferrite.