Synthesis and characterization of bulk amorphous steels

The corrosion behaviour of both crystalline and largely amorphous forms of the Fe-based glass forming alloy, Fe 43 Cr 16 Mo 16 C 15 B 10 alloy was investigated. Two different methods were used to induce transformation to the amorphous form of the alloy: laser melting and HVOF spraying. Both methods produced largely amorphous material, however the high brittleness of the alloy makes it susceptible to cracking during laser treatment, hence this technique is not suitable for largescale application. Potentiodynamic scanning showed that in 0.5M H 2 SO 4 and 3.5% NaCl electrolytes both amorphous forms of the alloy had better corrosion resistance (lower current densities for -200 to +1000mV SCE) compared to the crystalline material. The laser treated material and HVOF coating performed similarly in 3.5% NaCl. In 0.5M H 2 SO 4 the HVOF coating had a lower current density than the laser melted material for almost all of the potential range -300 to +1000mV SCE. The improved corrosion behaviour of the largely amorphous material is attributed to its homogeneity, and particularly to the elimination of the Mo-rich phase that underwent preferential corrosion in the crystalline form of the material.

Section: Microstructuresupporting

confidence: 74%

Corrosion behaviour of crystalline and amorphous forms of the glass forming alloy Fe43Cr16Mo16C15B10

Bakare

Voisey

Chokethawai

et al. 2012

“…So far, the investigated minor additions for Fe-based BMGs have included: (1) variations of the metalloid content (B [17], C [18], Si [19], P [20]), (2) rare earth additions such as Sm [21], Y [22,23], Er [24], Dy [25], Tb [26], and (3) transition metal additions such as Mo [27,28], Ni [29], Nb [30,31], Ta [31], Co [32], Cu [33]. In particular, addition of transition metals has been useful to develop new Fe-based BMGs with high GFA at low cost.…”

Section: Introductionmentioning

confidence: 99%

“…A detailed study of both the amorphous and partially crystallized state of Fe 50 Cr 15 Mo 14 C 15 B 6 [6] showed also the differential contribution to corrosion resistance of the different alloy elements. In order to enhance the relevance of Fe-Cr-Mo-C-B alloys for commercial applications and fundamental research, a great number of efforts have been devoted to improve the GFA by minor additions [20,21,[23][24][25]31]. The combination of high strength, hardness and corrosion resistance points this family of amorphous alloys as good candidates for protective amorphous coatings in highly corrosive environments.…”

Section: Introductionmentioning

confidence: 99%

Role of Nb in glass formation of Fe–Cr–Mo–C–B–Nb BMGs

Zhai

Pineda

Duarte

et al. 2014

Abstract:A new Fe-based bulk metallic glass with superior glass forming ability, Fe 46 Cr 15 Mo 14 C 15 B 6 Nb 4 , was developed based on the Fe-Cr-Mo-C-B alloy system by minor addition of niobium. The effects of niobium addition on glass formation of the Fe 50-x Cr 15 Mo 14 C 15 B 6 Nb x (x=0, 2, 4 and 6 at.%) alloys were investigated. The optimum addition content of niobium was determined as 4 at.% by X-ray diffraction and differential scanning calorimeter analysis. A fully amorphous rod sample with 3 mm in diameter was produced by using commercial-grade raw materials and a copper mold casting technique. This alloy shows an ultimate compressive strength of 1920 MPa and Vickers hardness 1360 HV, which is two to three times that of conventional high strength steel and suggests a promising potential for applications combining outstanding corrosion and wear resistance properties. The crystallization kinetics studies found that the activation energies for glass transition, onset of crystallization and crystallization peak were higher than those of other reported Fe-based bulk metallic glasses. The value of the fragility parameter m for the Fe 46 Cr 15 Mo 14 C 15 B 6 Nb 4 alloy was calculated to be 34, indicating that the Fe-Cr-Mo-C-B-Nb alloy system is a strong glass former according to the Angell's classification scheme. It is inferred that 2 the more sequential change in the atomic size, the generation of new atomic pairs with large negative heats of mixing and the amount of oxygen in the molten liquid neutralized into niobium oxides provide a synergetic effect for the remarkably improved glass-forming ability and thermal stability.

“…Amorphous Fe-based alloys including high-boron and carbon content in its composition (known as amorphous steels [2]) are regarded as having a high potential for industrial applications due to the high availability and low cost of the alloying elements [3]. These alloys have excellent magnetic and mechanical properties with fracture strengths as high as 4.4 GPa and plastic strain of 0.8% [4].…”

Section: Introductionmentioning

confidence: 99%

“…Recently their previous size limitation has been greatly overcome by adding a suitable amount of rare earth elements [2,3,5], thus increasing the production cost of the alloys, and many efforts have been carried out to understand the effect of various factors on the formation, thermal stability and properties of these alloys. In particular, the Fe-Cr-Mo-C-B system is widely studied due to its high glass-forming ability (GFA) and corrosion resistance in aggressive solutions [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Glass-formation and corrosion properties of Fe–Cr–Mo–C–B glassy ribbons with low Cr content

Madinehei

Bruna

Duarte

et al. 2014

The effect of low amounts of Cr on glass forming ability and corrosion behavior of Fe (65-x) Cr x Mo 14 C 15 B 6 (x=0, 2, 4, 6, 8, 10 at.%) ribbons have been studied. It was found that the reduced glass transition temperature (T rg ) do not change significantly with Cr content. The glass forming ability (GFA) of this system is evaluated by the  m ,  and  parameters and the alloys containing 4 and 6 at.% were found to be the best glass formers in this system. The temperature interval of the supercooled liquid region (∆T x ) changed with Cr and was enlarged from 35 K at x=0 to 50 K at x=4. Corrosion rates measured by immersion tests in H 2 SO 4 decreased with an increase of chromium content in the alloys. The electrochemical measurements indicate that the alloys containing more than 4 at.% of Cr are spontaneously passivated with low current densities in 0.1 N H 2 SO 4 whereas the alloys with Cr content < 4 at.% showed active behavior. In view of these results, the optimal amount of Cr addition in Fe-Mo-C-B amorphous steels is discussed.